High Efficiency Orthogonal Frequency Division Multiplexing (OFDM) Physical Layer (PHY)

ABSTRACT

In a method for generating a data unit for transmission via a communication channel, the data unit conforming to a first communication protocol, one or more orthogonal frequency division multiplexing (OFDM) symbols of the data unit are generated. Each OFDM symbol of the one or more OFDM symbols (i) occupies a first bandwidth, (ii) is generated with a first tone spacing, and (iii) includes a set of pilot tones. The first tone spacing is a fraction 1/N of a second tone spacing, the second tone spacing defined for the first bandwidth by a second communication protocol. The set of pilot tones includes a same number of pilot tones as defined for the first bandwidth by the second communication protocol. The data unit is generated to include the one or more OFDM symbols in a data portion of the data unit.

CROSS-REFERENCES TO RELATED APPLICATIONS

This disclosure claims the benefit of U.S. Provisional PatentApplication No. 62/006,522, entitled “High Efficiency OFDM PHY for WLAN802.11ax” and filed on Jun. 2, 2014, and U.S. Provisional PatentApplication No. 62/027,425, entitled “High Efficiency OFDM PHY for WLAN802.11ax” and filed on Jul. 22, 2014, the disclosures of both of whichare incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughputs, such as throughputs in the tens of Gbps range.

SUMMARY

In an embodiment, a method for generating a data unit for transmissionvia a communication channel, the data unit conforming to a firstcommunication protocol, includes generating, at a communication device,one or more orthogonal frequency division multiplexing (OFDM) symbols,wherein each OFDM symbol of the one or more OFDM symbols (i) occupies afirst bandwidth, (ii) is generated with a first tone spacing, and (iii)includes a set of pilot tones. The first tone spacing is a fraction 1/Nof a second tone spacing, the second tone spacing defined for the firstbandwidth by a second communication protocol, wherein N is a positiveinteger greater than one. The set of pilot tones includes a same numberof pilot tones as defined for the first bandwidth by the secondcommunication protocol. The method additionally includes generating, atthe communication device, the data unit to include the one or more OFDMsymbols in a data portion of the data unit.

In another embodiment, an apparatus comprises a network interface devicehaving one or more integrated circuits configured to generate one ormore orthogonal frequency division multiplexing (OFDM) symbols for adata unit that conforms to a first communication protocol, wherein eachOFDM symbol of the one or more OFDM symbols (i) occupies a firstbandwidth, (ii) are generated with a first tone spacing, and (iii)includes a set of pilot tones. The first tone spacing is a fraction 1/Nof a second tone spacing, the second tone spacing defined for the firstbandwidth by a second communication protocol, wherein N is a positiveinteger greater than one. The set of pilot tones includes a same numberof pilot tones as defined for the first bandwidth by the secondcommunication protocol. The one or more integrated circuits are furtherconfigured to generate the data unit to include the one or more OFDMsymbols in a data portion of the data unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment;

FIGS. 2A-2B are diagrams of physical layer (PHY) data units, accordingto several embodiments;

FIGS. 3A-3C are diagrams illustrating orthogonal frequency divisionmultiplexing (OFDM) tone spacing used with OFDM symbols of a PHY dataunit, according to several embodiments;

FIG. 4 is a diagram illustrating a guard interval used with an OFDMsymbol of a data unit, according to an embodiment;

FIG. 5 is a block diagram of a PHY processing unit, according to anembodiment;

FIG. 6 is a block diagram of another PHY processing unit, according toanother embodiment;

FIGS. 7-9 are tone maps corresponding to OFDM symbols, in severalembodiments;

FIG. 10 is a diagram of a PHY data unit, according to an embodiment;

FIG. 11 is a flow diagram of a method for generating a data unit,according to an embodiment;

FIG. 12 is a flow diagram of a method for generating a data unit,according to another embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least a first communicationprotocol. The first communication protocol is sometimes referred hereinas “high efficiency Wi-Fi,” “HEW” communication protocol, or IEEE802.11ax communication protocol. In some embodiments, different clientstations in the vicinity of the AP are configured to operate accordingto one or more other communication protocols which define operation inthe same frequency band as the HEW communication protocol but withgenerally lower data throughputs. The lower data throughputcommunication protocols (e.g., IEEE 802.11a, IEEE 802.11n, and/or IEEE802.11ac) are collectively referred herein as “legacy” communicationprotocols.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface device 16. The networkinterface device 16 includes a medium access control (MAC) processingunit 18 and a physical layer (PHY) processing unit 20. The PHYprocessing unit 20 includes a plurality of transceivers 21, and thetransceivers 21 are coupled to a plurality of antennas 24. Althoughthree transceivers 21 and three antennas 24 are illustrated in FIG. 1,the AP 14 includes other suitable numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments. In one embodiment,the MAC processing unit 18 and the PHY processing unit 20 are configuredto operate according to a first communication protocol (e.g., HEWcommunication protocol). In another embodiment, the MAC processing unit18 and the PHY processing unit 20 are also configured to operateaccording to a second communication protocol (e.g., IEEE 802.11acStandard). In yet another embodiment, the MAC processing unit 18 and thePHY processing unit 20 are additionally configured to operate accordingto the second communication protocol, a third communication protocoland/or a fourth communication protocol (e.g., the IEEE 802.11a Standardand/or the IEEE 802.11n Standard).

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 includes othersuitable numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the first communication protocol. In some embodiments, atleast one of the client stations 25 is not configured to operateaccording to the first communication protocol but is configured tooperate according to at least one of the second communication protocol,the third communication protocol and/or the fourth communicationprotocol (referred to herein as a “legacy client station”).

The client station 25-1 includes a host processor 26 coupled to anetwork interface device 27. The network interface device 27 includes aMAC processing unit 28 and a PHY processing unit 29. The PHY processingunit 29 includes a plurality of transceivers 30, and the transceivers 30are coupled to a plurality of antennas 34. Although three transceivers30 and three antennas 34 are illustrated in FIG. 1, the client station25-1 includes other suitable numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 30 and antennas 34 in other embodiments.

According to an embodiment, the client station 25-4 is a legacy clientstation, i.e., the client station 25-4 is not enabled to receive andfully decode a data unit that is transmitted by the AP 14 or anotherclient station 25 according to the first communication protocol.Similarly, according to an embodiment, the legacy client station 25-4 isnot enabled to transmit data units according to the first communicationprotocol. On the other hand, the legacy client station 25-4 is enabledto receive and fully decode and transmit data units according to thesecond communication protocol, the third communication protocol and/orthe fourth communication protocol.

In an embodiment, one or both of the client stations 25-2 and 25-3, hasa structure the same as or similar to the client station 25-1. In anembodiment, the client station 25-4 has a structure similar to theclient station 25-1. In these embodiments, the client stations 25structured the same as or similar to the client station 25-1 have thesame or a different number of transceivers and antennas. For example,the client station 25-2 has only two transceivers and two antennas,according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 isconfigured to generate data units conforming to the first communicationprotocol and having formats described herein. The transceiver(s) 21is/are configured to transmit the generated data units via theantenna(s) 24. Similarly, the transceiver(s) 24 is/are configured toreceive data units via the antenna(s) 24. The PHY processing unit 20 ofthe AP 14 is configured to process received data units conforming to thefirst communication protocol and having formats described herein and todetermine that such data units conform to the first communicationprotocol, according to various embodiments.

In various embodiments, the PHY processing unit 29 of the client device25-1 is configured to generate data units conforming to the firstcommunication protocol and having formats described herein. Thetransceiver(s) 30 is/are configured to transmit the generated data unitsvia the antenna(s) 34. Similarly, the transceiver(s) 30 is/areconfigured to receive data units via the antenna(s) 34. The PHYprocessing unit 29 of the client device 25-1 is configured to processreceived data units conforming to the first communication protocol andhaving formats described hereinafter and to determine that such dataunits conform to the first communication protocol, according to variousembodiments.

FIG. 2A is a diagram of a physical layer (PHY) orthogonal frequencydivision multiplexing (OFDM) data unit 200 that the AP 14 is configuredto transmit to a client station (e.g., the client station 25-1),according to an embodiment. In an embodiment, the client station 25-1 isalso configured to transmit the data unit 200 to the AP 14. The dataunit 200 conforms to the HEW communication protocol and occupies a 20MHz bandwidth. Data units similar to the data unit 200 occupy othersuitable bandwidth such as 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz,for example, or other suitable bandwidths, in other embodiments. Thedata unit 200 is suitable for “mixed mode” situations, i.e., when theWLAN 10 includes a client station (e.g., the legacy client station 25-4)that conforms to a legacy communication protocol, but not the firstcommunication protocol. The data unit 200 is utilized in othersituations as well, in some embodiments.

The data unit 200 includes a preamble 202, which, in turn, includes alegacy preamble portion 203 and a high efficiency WLAN (HEW) preambleportion 204. The legacy preamble portion 202 includes an L-STF 205, anL-LTF 210, and an L-SIG 215. The HEW preamble portion 203 includes oneor more HEW signal field(s) (HEW-SIGA(s)) 220, an HEW short trainingfield (HEW-STF) 225, M HEW long training fields (HEW-LTFs) 230, where Mis an integer, and an HEW signal field B (HEW-SIGB) 235. Each of theL-STF 205, the L-LTF 210, the L-SIG 215, the HEW-SIGAs 220, the HEW-STF225, the M HEW-LTFs 230, and the HEW-SIGB 235 comprises an integernumber of one or more OFDM symbols. For example, in an embodiment, theHEW-SIGAs 220 comprise two OFDM symbols, and the HEW-SIGB fieldcomprises one OFDM symbol, in an embodiment. The L-SIG 215, theHEW-SIGAs 220 and the HEW-SIGB 235 generally carry formattinginformation for the data unit 200, in an embodiment. In someembodiments, the data unit 200 also includes a data portion (HEW-DATA)240.

In the embodiment of FIG. 2A, the data unit 200 includes one of each ofthe L-STF 205, the L-LTF 210, the L-SIG 215, and the HEW-SIGA(s) 220. Inother embodiments in which an OFDM data unit similar to the data unit200 occupies a cumulative bandwidth other than 20 MHz, each of the L-STF205, the L-LTF 210, the L-SIG 215, the HEW-SIGA(s) 220 is repeated overa corresponding number of 20 MHz sub-bands of the whole bandwidth of thedata unit, in an embodiment. For example, in an embodiment, the OFDMdata unit occupies an 80 MHz bandwidth and, accordingly, includes fourof each of the L-STF 205, the L-LTF 210, the L-SIG 215, the HEW-SIGA(s)220. In some embodiments, the modulation of different 20 MHz sub-bandssignals is rotated by different angles. For example, in one embodiment,all OFDM tones within a first subband are rotated 0-degrees, all OFDMtones within a second subband is rotated 90-degrees, a third sub-band isrotated 180-degrees, and a fourth sub-band is rotated 270-degrees. Inother embodiments, different suitable rotations are utilized. Thedifferent phases of the 20 MHz sub-band signals result in reduced peakto average power ratio (PAPR) of OFDM symbols in the data unit 200, inat least some embodiments. In an embodiment, if the data unit thatconforms to the first communication protocol is an OFDM data unit thatoccupies a cumulative bandwidth such as 20 MHz, 40 MHz, 80 MHz, 160 MHz,320 MHz, 640 MHz, etc., the HEW-STF, the HEW-LTFs, the HEW-SIGB and theHEW data portion occupy the corresponding whole bandwidth of the dataunit.

In an embodiment, the first communication protocol utilizes the samechannelization scheme as defined by a legacy communication protocol. Forexample, the first communication protocol utilizes the samechannelization scheme as defined in the IEEE 802.11ac Standard. In thisembodiment, the first communication protocol operates with 20 MHz, 40MHz, 80 MHz and 160 MHz communication channels. The 20 MHz, 40 MHz, 80MHz and 160 MHz communication channels coincide, e.g., in centerfrequencies, with the channels utilized by a legacy communicationprotocol (e.g., the IEEE 802.11ac Standard). In an embodiment, however,the first communication protocol defines a tone spacing that isdifferent that the tone spacing defined by the legacy communicationprotocol (e.g., the IEEE 802.11ac Standard). For example, the firstcommunication protocol defines a tone spacing that is a fraction 1/N ofthe tone spacing defined by the legacy communication protocol, where Nis a suitable integer greater than one, in an embodiment. The integer Nis an even integer (e.g., 2, 4, 6, 8, 10, etc.), in an embodiment. Theinteger N is an integer that corresponds to a power of two (e.g., 2, 4,8, 16, etc.), in an embodiment. The reduced tone spacing is used in thefirst communication protocol to improve communication range compared tocommunication range supported or achieved by a legacy communicationprotocol, in an embodiment. Additionally or alternatively, the reducedtone spacing is used is the first communication protocol to increasethroughput compared to throughput achieved in a same bandwidth channelby a legacy communication protocol.

FIG. 2B is a diagram of an example orthogonal frequency divisionmultiple access (OFDMA) data unit 250, according to an embodiment. TheOFDMA data unit 250 includes a plurality of OFDM data unit 252-1, 252-2and 252-3. In an embodiment, the AP 14 transmits the OFDM data units252-1, 252-2, 252-3 to different client stations 25 via respective OFDMsub-channels within the OFDMA data unit 250. In another embodiment,different client stations 25 transmit respective OFDM data units 252-1,252-2, 252-3 to the AP 14 in respective OFDM sub-channels within theOFDMA data unit 250. In this embodiment, The AP 14 receives the OFDMdata units 252-1, 252-2, 252-3 from the client stations 25 viarespective OFDM sub-channels of within the OFDMA data unit 250, in thisembodiment.

Each of the OFDM data units 252-1, 252-2, 252-3 conforms to acommunication protocol that supports OFDMA transmission, such as the HEWcommunication protocol, in an embodiment. In an embodiment in which theOFDMA data unit 250 corresponds to a downlink OFDMA data unit, the OFDMAdata unit 250 is generated by the AP 14 such that each OFDM data unit252 is transmitted to a respective client station 25 via a respectivesub-channel of the WLAN 10 allocated for downlink transmission of theOFDMA data unit 250 to the client station. Similarly, an embodiment inwhich the OFDMA data unit 250 corresponds to an uplink OFDMA data unit,the AP 14 receives the OFDM data units 252 via respective sub-channelsof the WLAN 10 allocated for uplink transmission of the OFDM data units252 from the client stations, in an embodiment. For example, the OFDMdata unit 252-1 is transmitted via a first 20 MHZ sub-channel of theWLAN 10, the OFDM data unit 252-2 is transmitted via a second 20 MHzsub-channel of the WLAN 10, and the OFDM data unit 252-3 is transmittedvia a 40 MHz sub-channel of the WLAN 10, in the illustrated embodiment.

In an embodiment, each of the OFDM data units 252 includes a preambleincluding one or more legacy short training fields (L-STF) 254, one ormore legacy long training fields (L-LTF) 256, one or more legacy signalfields (L-SIG) 258, one or more first high efficiency WLAN signal field(HEW-SIG-A) 260, N HEW long training fields (HEW-LTF) and a second HEWsignal field (HEW-SIGB) 264. Additionally, each OFDM data unit 252includes a high efficiency WLAN data portion (HEW-DATA) 268. In anembodiment, each L-LSF field 256, each L-LTF field 258, each L-SIG field260 and each HEW-SIGA field 262 occupies a smallest bandwidth supportedby the WLAN 10 (e.g., 20 MHz). In an embodiment, if an OFDM data unit252 occupies a bandwidth that is greater than the smallest bandwidth ofthe WLAN 10, then each L-LSF field 256, each L-LTF field 258, each L-SIGfield 260 and each HEW-SIGA field 262 is duplicated in each smallestbandwidth portion of the OFDM data unit 252 (e.g., in each 20 MHzportion of the data unit 252). On the other hand, each HEW-STF field262, each HEW-LTF field 264, each HEW-SIGB field 266 and each HEW dataportion 268 occupies an entire bandwidth of the corresponding OFDM dataunit 252, in an embodiment. For example, the OFDM data unit 252-3occupies 40 MHz, wherein L-LSF field 256, the L-LTF field 258, L-SIGfield 260 and HEW-SIGA fields 262 is duplicated in the upper and thelower 20 MHz bands of the OFDM data unit 252-3, while each of theHEW-STF field 262, each of the HEW-LTF fields 264, each of the HEW-SIGBfield 266 and each of the HEW data portion 268 occupies the entire 40MHz bandwidth of the data unit 252, in the illustrated embodiment.

In some embodiments, data for different client stations 25 istransmitted using respective sets of OFDM tones assigned to the clientstations 25, wherein a set OFDM tones assigned to a client station 25may correspond to a bandwidth that is smaller than the smallest channelof the WLAN 10. For example, a set of OFDM tones assigned to a clientstation 25 corresponds to a bandwidth that is smaller than 20 MHz (e.g.,5 MHz, 10 MHz, 15 MHz, or any other suitable bandwidth less than 20MHz), in an embodiment. In an embodiment, if an OFDM data unit 252occupies a bandwidth that is smaller than the smallest bandwidth of theWLAN 10, then each L-LSF field 256, each L-LTF field 258, each L-SIGfield 260 and each HEW-SIGA field 262 nonetheless occupies the entiresmallest bandwidth portion of the OFDM data unit 252 (e.g., in 20 MHzportion of the data unit 252). On the other hand, each HEW-STF field262, each HEW-LTF field 264, each HEW-SIGB field 266 and each HEW dataportion 268 occupies the smaller bandwidth of the corresponding OFDMdata unit 252, in an embodiment. Generally, a data unit 252 correspondsto any suitable number of OFDM tones within the data unit 250, in anembodiment.

A set of OFDM tones corresponding to a client station 25 is sometimesreferred to herein as a “resource unit (RU)”. In an embodiment, eachOFDM data unit 252 corresponds to a client station 25 and to a resourceunit assigned to the client station 25. In various embodiments, an RUcorresponding to a client station 25 includes a suitable number of OFDMtones within the data unit 250. For example, an RU includes 26, 52, 106,242, 484 or 996 OFDM tones, in some embodiments and/or scenarios. Inother embodiments, an RU includes other suitable numbers of OFDM tones.

In an embodiment, padding is used in one or more of the OFDM data units252 to equalize lengths of the OFDM data units 252. Accordingly, thelength of each of the OFDM data units 252 correspond to the length ofthe OFDMA data unit 252, in this embodiment. Ensuring that the OFDM dataunits 252 are of equal lengths synchronizes transmission ofacknowledgment frames by client stations 25 that receive the data units252, in an embodiment. In an embodiment, each of one or more of the OFDMdata units 252 is an aggregate MAC service data units (A-MPDU), which isin turn included in a PHY protocol data unit (PPDU). In an embodiment,padding (e.g., zero-padding) within one or more of the A-MPDUs 252 isused to equalize the lengths of the data units 252, and to synchronizetransmission of acknowledgement frames corresponding to the OFDMA dataunit 250.

FIGS. 3A-3C are diagrams illustrating OFDM tone spacing used with OFDMsymbols of a data unit, such as the data unit 200 of FIG. 2A or the dataunit 250 of FIG. 2B, in some embodiments. Turning first to FIG. 3A, atone spacing 300 corresponds to tone spacing defined in a legacycommunication protocol. For example, the tone spacing 300 corresponds tothe tone spacing defined in the IEEE 802.11ac Standard, in anembodiment. In an embodiment, an OFDM symbol generated with the tonespacing 300 for a particular bandwidth is generated using an InverseDigital Fourier Transform (IDFT) size that results in a tone spacing(TS) of 312.5 kHz in the particular bandwidth. For example, an OFDMsymbol generated with the tone spacing 300 for a 20 MHz bandwidth isgenerated using a 64 point IDFT, resulting in the tone spacing (TS) of312.5 kHz, in an embodiment. Similarly, an OFDM symbol generated withthe tone spacing 300 for a 40 MHz bandwidth is generated using a 128point IDFT, an OFDM symbol generated with the tone spacing 300 for an 80MHz bandwidth is generated using a 256 point IDFT, an OFDM symbolgenerated with the tone spacing 300 for a 160 MHz bandwidth is generatedusing a 512 point IDFT, etc., in an embodiment. Alternatively, in someembodiments, an OFDM symbol generated for at least some of the channelbandwidths is generated using an IDFT size that results in a tonespacing (TS) of 312.5 kHz in a sub-band of the entire bandwidth. In suchembodiments, multiple sub-bands of the OFDM symbol are individuallygenerated using the IDFT size that results in the tone spacing (TS) of312.5 kHz in the individual sub-bands. For example, an OFDM symbol for a160 MHz-wide channel is generated using a 256 point IDFT in each one ofthe two 80 MHz sub-bands of the 160 MHz-wide channel, in an embodiment.

Turning now to FIG. 3B, a tone spacing 320 is reduced by a factor 2 (½)with respect to the tone spacing 300 of FIG. 3A. For example, continuingwith the example above, whereas on OFDM symbol generated with the tonespacing 300 for a 20 MHz bandwidth is generated using a 64 point IDFT,an OFDM symbol generated with the tone spacing 320 for a 20 MHzbandwidth is generated using a 128 point IDFT, resulting in the ½ of thetone spacing 300 of FIG. 3A (i.e., 156.25 kHz). Similarly, an OFDMsymbol generated with the tone spacing 320 for a 40 MHz-wide channel isgenerated using a 256 point IDFT, an OFDM symbol generated with the tonespacing 320 for an 80 MHz bandwidth channel is generated using a 512point IDFT, an OFDM symbol generated with the tone spacing 320 for a 160MHz bandwidth channel is generated using a 1024 point IDFT, etc., in anembodiment. Alternatively, in some embodiments, an OFDM symbol generatedfor at least some of the channel bandwidths is generated using an IDFTsize that results in a tone spacing (TS) of 156.25 kHz in a sub-band ofthe entire bandwidth. In such embodiments, multiple sub-bands of theOFDM symbol are individually generated with the IDFT size that resultsin the tone spacing (TS) of 312.5 kHz in the individual sub-bands. Forexample, an OFDM symbol for a 160 MHz bandwidth channel is generatedusing a 512 point IDFT in each one of the two 80 MHz sub-bands of the160 MHz bandwidth channel, in an embodiment.

Turning now to FIG. 3C, a tone spacing 350 is reduced by a factor 4 (¼)with respect to the tone spacing 300 of FIG. 3A. For example, continuingagain with the example above, whereas an OFDM symbol generated with thetone spacing 300 for a 20 MHz bandwidth is generated using a 64 pointIDFT, an OFDM symbol generated with the tone spacing 350 for a 20 MHzbandwidth is generated using a 256 point IDFT, resulting in the ¼ of thetone spacing 300 of FIG. 3A (i.e., 78.125 kHz), in an embodiment.Similarly, an OFDM symbol generated with the tone spacing 350 for a 40MHz bandwidth channel is generated using a 512 point IDFT, an OFDMsymbol generated with the tone spacing 350 for an 80 MHz bandwidthchannel is generated using a 1024 point IDFT, an OFDM symbol generatedwith the tone spacing 350 for a 160 MHz bandwidth channel is generatedusing a 2048 point IDFT, etc., in an embodiment. Alternatively, in someembodiments, an OFDM symbol generated for at least some of the channelbandwidths is generated using an IDFT size that results in a tonespacing (TS) of 78.125 kHz in a sub-band of the entire bandwidth. Insuch embodiments, multiple sub-bands of the OFDM symbol are individuallygenerated with the IDFT size that results in the tone spacing (TS) of312.5 kHz in the individual sub-bands. For example, an OFDM symbol for a160 MHz bandwidth channel is generated using a 512 point IDFT each oneof the 80 MHz sub-bands of the 160 MHz bandwidth channel, in anembodiment. As just another example, an OFDM symbol for a 40 MHzbandwidth channel is generated using a 256 point IDFT in each one of the20 MHz sub-bands of the 40 MHz bandwidth channel, in an embodiment. Asyet another example, in yet another embodiment, an OFDM symbol for an 80MHz bandwidth channel is generated using a 256 point IDFT in each one ofthe four 20 MHz sub-bands of the 80 MHz bandwidth channel, in anembodiment.

A tone spacing defined in a legacy communication protocol, such as thetone spacing 300 of FIG. 3A, is sometimes referred to herein as “normaltone spacing” and a tone spacing that is smaller than the tone spacingdefined by the legacy communication protocol, such as the tone spacing320 of FIG. 3B and the tone spacing 350 of FIG. 3C is sometimes referredto herein as “reduced tone spacing.”

Generally speaking symbol duration of an OFDM symbols, in time, isinversely proportional to the tone spacing used with the OFDM symbol.That is, if Δf corresponds to the tone spacing used with an OFDM symbol,then the time symbol duration of the OFDM symbol is T=1/Δf. Accordingly,a relatively smaller tone spacing used with an OFDM symbol results in arelatively larger symbol duration of the OFDM symbol, and vice versa, inan embodiment. For example, a tone spacing of Δf=312.5 kHz as in FIG. 3Aresults in an OFDM symbol duration of 3.2 μs, while a tone spacing ofΔf=156.25 kHz as in FIG. 3B results in an OFDM symbol duration of 6.4μs, in an embodiment. Further, a sampling rate at which a receivingdevice needs to sample the OFDM symbol is inversely proportional to theIDFT size (number of points) used to generate the OFDM symbol. Inparticular, in an embodiment, if N_(fft) is the IDFT size used togenerate the OFDM symbol, then the sampling rate at which the receivingdevice needs to sample the OFDM symbol is T/N_(fft), where T is the OFDMsymbol duration (T=1/Δf).

In an embodiment, the first communication protocol defines a set ofguard intervals of different lengths that may be used with OFDM symbolsto prevent or minimize intersymbol interference at the receiver causedby multipath propagation in the communication channel. Generallyspeaking, a sufficiently long guard interval is needed to mitigateinterference based on the delay spread of the particular channel beingutilized, in an embodiment. On the other hand, a relatively shorterguard interval, particularly in terms of a ratio of the guard intervalrelative to a length of the OFDM symbol and, accordingly, amount of“useful” data that can be transmitted in the OFDM symbol, generallyresults in a smaller overhead associated with the guard interval andimproves overall throughput, in an embodiment.

FIG. 4 is a diagram illustrating a guard interval used with an OFDMsymbol of a data unit, such as the data unit 200 of FIG. 2A or the dataunit 250 of FIG. 2B, according to an embodiment. In an embodiment, aguard interval portion 402 is pre-pended to an information portion ofthe OFDM symbol 404. In an embodiment, the guard interval comprises acyclic prefix repeating an end portion of the information portion 504.In an embodiment, the guard interval portion 402 is used to ensureorthogonality of OFDM tones at a receiving device (e.g., the clientstation 25-1) and to minimize or eliminate inter-symbol interference dueto multi-path propagation in the communication channel via which theOFDM symbol is transmitted.

According to an embodiment, the length of the guard interval portion 402to be used with particular OFDM symbols of the data unit 200 is selectedfrom a set of guard intervals supported by the HEW communicationprotocol. For example, the set of guard intervals supported by the HEWcommunication protocol includes 0.4 μs, 0.8 μs, 1.6 μs, and 3.2 μs guardintervals. In other embodiments, the set of guard intervals supported bythe HEW communication protocol exclude one or more of 0.4 μs, 0.8 μs,1.6 μs, and 3.2 μs and/or include one or more suitable guard intervalsother than 0.4 μs, 0.8 μs, 1.6 μs, and 3.2 μs instead of or in additionto the guard intervals 0.4 μs, 0.8 μs, 1.6 μs, and 3.2 μs. In anembodiment, in accordance with terminology used in a legacycommunication protocol (e.g., the IEEE 802.11n Standard or the IEEE802.11ac Standard), a guard interval of 0.8 μs is sometimes referred toherein as a “normal guard interval” and a guard interval of 0.4 μs issometimes referred to herein as “short guard interval.”

In an embodiment, the first communication protocol defines at least afirst transmission mode (e.g. normal mode) the utilizes the normal tonespacing and supports guard intervals defined by a legacy communicationprotocol (e.g., the IEEE 802.11ac Standard) and a second transmissionmode (e.g., a high efficiency mode) that utilizes a reduced tone spacingand/or a larger guard interval compared to the tone spacing and guardintervals of the legacy communication protocol. For example, the normalmode utilizes the normal tone spacing 300 of FIG. 3 A and supports 0.4μs and 0.8 μs guard intervals, in an embodiment. The high efficiencymode, on the other hand, utilizes the ¼ tone spacing 350 of FIG. 3C andsupports two or more of (e.g., two of, three of, four of, etc.) 0.4 μs,0.8 μs, 1.6 μs, 2.4 μs and 3.2 μs guard interval options or othersuitable guard interval options, in an example embodiment.Alternatively, in another embodiment, the first communication protocoldefines a normal mode that utilizes a reduced tone spacing (e.g., ½ tonespacing or ¼ tone spacing) and supports two or more of (e.g., two of,three of, four of, etc.) 0.4 μs, 0.8 μs, 1.6 μs, 2.4 μs and 3.2 μs guardinterval options or other suitable guard interval options.

In an embodiment, the particular transmission mode being used with adata unit, such as the data unit 200 of FIG. 2A or the data unit 250 ofFIG. 2B, is signaled to a receiving device via a mode indicationincluded in the preamble of the data unit. For example, referring to thedata unit 200 of FIG. 2A, the HEW-SIGA field 220 or the HEW-SIGB field235 includes an indication of the transmission mode used with the dataunit 200, in an embodiment. In another embodiment, the preamble of adata unit, such as the data unit 200 of FIG. 2A or the data unit 250 ofFIG. 2B, is formatted such that a receiving device can auto-detecttransmission mode used with the data unit 200 based on modulation (e.g.,binary phase shift keying (BPSK) verses binary phase shift keyingshifted by 90 degrees (Q-BPSK)) of one or more fields of the preamble ofthe data unit 200.

In some embodiments, some of the OFDM symbols of a data unit such as thedata unit 200 of FIG. 2A or the data unit 250 of FIG. 2B are generatedusing the normal tone spacing and the regular guard interval (e.g., 0.8μs) of a legacy communication protocol (e.g., the IEEE 802.11acStandard), while other OFDM symbols of the data unit are generated usinga reduced tone spacing (e.g., the ½ tone spacing 320 of FIG. 3B or thetone spacing 350 of FIG. 3C) and/or using a longer guard intervalcompared to guard intervals supported by the legacy communicationprotocol. For example, referring to FIG. 2A, the L-STF 205, the L-LTF210, the L-SIG 215, the HEW-SIGA 220 and the HEW-STF field 225 aregenerated using the using the normal tone spacing and the regular guardinterval (e.g., 0.8 μs) of the IEEE 802.11ac Standard, while theHEW-LTFs 230, the HEW-SIGB 235 and the data portion 240 are generatedusing a reduced tone spacing (e.g., the ½ tone spacing 320 of FIG. 3B orthe tone spacing 350 of FIG. 3C) and/or using a longer guard intervalcompared to guard intervals supported by the IEEE 802.11ac Standard, inan embodiment. As another example, in another embodiment, the L-STF 205,the L-LTF 210, the L-SIG 215 and the HEW-SIGA 220 are generated usingthe using the normal tone spacing and the regular guard interval (e.g.,0.8 μs) of the IEEE 802.11ac Standard, the HEW-STF field is generatedusing the normal tone spacing and a longer guard interval compared tothe guard intervals supported by the IEEE 802.11ac Standard, and theHEW-LTFs 230, the HEW-SIGB 235 and the data portion 240 are generatedusing a reduced tone spacing (e.g., the ½ tone spacing 320 of FIG. 3B orthe tone spacing 350 of FIG. 3C) and/or using a longer guard intervalcompared to guard intervals supported by the IEEE 802.11ac Standard.

FIG. 5 is a block diagram of a transmit portion of an example PHYprocessing unit 500 configured to generate data units, such as the dataunit 200 of FIG. 2A or the data unit 250 of FIG. 2B, that conform to thefirst communication protocol, according to an embodiment. Referring toFIG. 1, the PHY processing unit 20 of AP 14 and the PHY processing unit29 of client station 25-1 are each similar to or the same as PHYprocessing unit 500, in one embodiment. The PHY processing unit 500 isconfigured to generate data units such as the data unit 200 of FIG. 2Aor the data unit 250 of FIG. 2B, in an embodiment. In other embodiments,however, the PHY processing unit 500 is configured to generate suitabledata units different from the data unit 200 of FIG. 2A or the data unit250 of FIG. 2B. Similarly, suitable PHY processing units different fromthe PHY processing unit 400 is configured to generate data unit such asthe data unit 200 of FIG. 2A or the data unit 250 of FIG. 2B, in someembodiments.

In an embodiment, the PHY processing unit 500 includes a processing path501, which in turn includes a PHY padding unit 502, a scrambler 506, anencoder parser 510, one or more forward error correction (FEC) encoders512, a stream parser 516, segment parsers 518, BCC interleavers 502,constellation mappers 522, LDPC tone mappers 526, segment deparsers 528,a space-time block coding (STBC) unit 530, cyclic shift diversity (CSD)units 532 and a spatial mapping unit 536. The various components of theprocessing path 501, according to some embodiments, are described inmore detail below. Some of the components of the processing path 501 arebypassed or omitted, as described in more detail below, in someembodiments. Further, in an embodiment in which the processing unit 500is configured to generate OFDMA data units such as the data unit 25 ofFIG. 2B, the PHY processing unit 500 includes multiple processing paths501, each processing path 501 corresponding to a particular clientstation to which the OFDMA data unit is to be transmitted, in anembodiment. More generally, in an embodiment, a processing path 501 ofthe PHY processing unit 500 corresponds to a subset of OFDM tones, or aresource unit, assigned to a client station 25.

In an embodiment, the padding unit 502 of the processing path 501 addsone or more padding bits to an information bit stream prior to providingthe information bit stream to the scrambler 506, according to anembodiment. The scrambler 506 generally scrambles the information bitstream to reduce occurrences of long sequences of ones or zeros, in anembodiment. The encoder parser 510 is coupled to the scrambler 506. Theencoder parser 510 demultiplexes the information bit stream into one ormore encoder input streams corresponding to one or more FEC encoders512.

While three FEC encoders 512 are shown in FIG. 5, different numbers ofFEC encoders are included, and/or different numbers of FEC encodersoperate in parallel, in various embodiments and/or scenarios. Forexample, according to one embodiment, the PHY processing unit 500includes four FEC encoders 512, and one, two, three, or four of the FECencoders 512 operate simultaneously depending on the particularmodulation and coding scheme (MCS), bandwidth, and number of spatialstreams. Each FEC encoder 512 encodes the corresponding input stream togenerate a corresponding encoded stream. In one embodiment, each FECencoder 512 includes a binary convolutional coder (BCC). In anotherembodiment, each FEC 512 encoder includes a BCC followed by a puncturingblock. In another embodiment, each FEC encoder 512 includes a lowdensity parity check (LDPC) encoder. In some embodiments in which LDPCencoding is utilized, only one encoder 512 is utilized to encode the bitinformation stream, and the encoder parser 510 is bypassed or omitted.

A stream parser 516 parses the one or more encoded streams into one ormore spatial streams for separate interleaving and mapping intoconstellation points/symbols. In one embodiment, the stream parser 516operates according to the IEEE 802.11ac Standard, such that thefollowing equation is satisfied:

$\begin{matrix}{s = {\max \{ {1,\frac{N_{BPSCS}}{2}} \}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where s is the number of coded bits assigned to a single axis in aconstellation point for each of N_(SS) spatial streams, and whereN_(BPSCS) is the number of bits per subcarrier. For each FEC encoder 512(whether BCC or LDPC), consecutive blocks of s coded bits are assignedto different spatial streams in a round robin fashion, in an embodiment.In some embodiments where the set of FEC encoders 512 includes two ormore BCC encoders, the outputs of the individual FEC encoders 512 areused in an alternating fashion for each round-robin cycle, i.e.,initially S bits from the first FEC encoder 512 are fed into N_(SS)spatial streams, then S bits from the second FEC encoder 106 are fedinto the N_(SS) spatial streams, and so on, where:

S=N _(SS) ×s  Equation 2

Corresponding to each of the N_(SS) spatial streams, a segment parser518 parses the coded bits into multiple segments. In an embodiment, eachsegment parser 518 parses coded bits at an output of the stream parser516 into a plurality of segments corresponding to a plurality offrequency sub-bands of the communication channel for which the data unitis being generated. As just an illustrative example, for a 40 MHz widecommunication channel, each segment parser 518 parses coded bits at anoutput of the stream parser 518 to two segments corresponding to two 20MHz frequency sub-bands of the 40 MHz channel. As another example, for a160 MHz communication channel, each segment parser 518 parses coded bitsat an output of the stream parser 516 to two segments corresponding totwo 80 MHz frequency sub-bands of the 160 MHz channel, in an embodiment.Although each segment parser 518 is illustrated in FIG. 5 as a twosegment parser having two outputs, each segment parser 518 parses codedbits into a number of segments greater than two, in some embodiments.For example, for an 80 MHz wide communication channel, each segmentparser 518 parses coded bits at an output of the stream parser 516 tofour segments corresponding to four 20 MHz frequency sub-bands of the 80MHz channel, in an embodiment. As another example, for a 160 MHzcommunication channel, a segment parser 518 parses coded bits at anoutput of the stream parser 516 to eight segments corresponding to eight20 MHz frequency sub-bands of the 160 MHz channel, in an embodiment.

In an embodiment, the segment parsers 518 are utilized in only sometransmission modes (e.g., corresponding to only some channelbandwidths), and are bypassed or omitted in other transmission modes(e.g., for other channel bandwidths). For example, in an embodiment, thesegment parsers 518 are utilized in transmission modes corresponding toa communication channel having a 40 MHz bandwidth and to a communicationchannels having a 160 MHz, and are bypassed or omitted in transmissionmodes corresponding to a communication channel having a 20 MHz bandwidthand to a communication channels having a 80 MHz, in an embodiment. Asanother example, the segment parsers 518 are utilized in a transmissionmode corresponding to a communication channel having a 160 MHzbandwidth, and are bypassed or omitted in transmission modescorresponding to communication channels having a 20 MHz bandwidth, a 40MHz bandwidth and an 80 MHz bandwidth, in another embodiment. In otherembodiments, however, the segment parsers 518 are utilized and/or arebypassed in transmission modes corresponding to other suitable channelbandwidths.

Coded bits corresponding to each spatial stream and each segment areoperated on by a respective BCC interleaver 520, in an embodiment. In anembodiment, an interleaver 520, corresponding to a spatial stream and asegment, interleaves bits (i.e., changes the order of the bits) of thespatial stream and the segment to prevent long sequences of adjacentnoisy bits within the spatial stream and the segment from entering adecoder at the receiver. More specifically, the interleaver 520 mapsadjacent coded bits onto non-adjacent locations in the frequency domainor in the time domain. The interleaver 520 performs two frequencypermutations in each data stream, and a third permutation to cyclicallyshift bits differently on different streams, in an embodiment. Theparameters N_(col), N_(row), and N_(rot) (i.e., number of columns,number of rows, and frequency rotation parameter, respectively) used bythe interleaver 520 are suitable values based on the bandwidth of thedata unit being generated and the FFT size to be utilized for generatingthe data unit, in various embodiments. In an embodiment, the firstpermutation by the interleaver 520 ensures that adjacent coded bits aremapped onto non-adjacent sub-carriers of the signal. The secondpermutation performed by the interleaver 520 ensures that adjacent codedbits are mapped alternatively onto less and more significant bits of theconstellation to avid long sequences of low reliability bits, in anembodiment. Further the third permutation is performed by theinterleaver 520 in embodiments with multiple spatial streams, and thethird permutation, in an embodiment, performs a different frequencyrotation on respective different spatial streams.

In an embodiment, the parameters N_(col), N_(row), and N_(rot) utilizedby the BCC interleavers 520 for an OFDM symbol being generated for a 20MHz-wide channel correspond to N_(col), N_(row), and N_(rot),respectively, defined by the IEEE 802.11ac Standard for an 80 MHzcommunication channel. Similarly, in an embodiment in which two segmentsof coded bits for a 40 MHz communication channel are respectivelyoperated on by two BCC interleaver 520, the parameters N_(col), N_(row),and N_(rot) for an OFDM symbol being generated for a 40 MHz-wide channelcorrespond to N_(col), N_(row), and N_(rot), respectively, used for a 20MHz-wide channel of the first communication protocol (e.g., the N_(col),N_(row), and N_(rot), parameters defined for an 80 MHz communication bythe IEEE 802.11ac Standard), in an embodiment. On the other hand, in anembodiment in which an OFDM symbol for a 40 MHz channel is generatedusing a single segment of coded bits (e.g., the segment parsers 518 areomitted or bypassed), new (e.g., not previously defined in the IEEE802.11ac Standard) N_(col), N_(row), and N_(rot) parameters defined bythe first communication protocol for a communication channel having a 40MHz bandwidth are utilized. In an embodiment, the new N_(col), N_(row),and N_(rot), parameters are scaled versions of the correspondingN_(col), N_(row), and N_(rot), parameters defined for a 40 MHz channelby a legacy communication protocol (e.g., the IEEE 802.11ac Standard).For example, in an illustrative embodiment, the new N_(col) and N_(row)parameters correspond to the N_(col) and N_(row) parameters,respectively, defined for 40 MHz channel in the IEEE 802.11ac Standardscaled at least approximately by sqrt(N), where sqrt ( ) is a squareroot function and N is the factor by which the tone spacing is reducedfor the 40 MHz bandwidth in the first communication protocol. Further,in an embodiment, one or both of N_(col) and N_(row) are adjusted such aproduct of N_(col) and N_(row) corresponds to a number of data tones inthe 40 MHz bandwidth, in an embodiment. Referring now to the N_(rot)parameter, N_(rot) corresponds to the N_(rot) parameter defined for 40MHz bandwidth by the IEEE 802.11ac Standard scaled by N_(rot) in anexample embodiment. In other embodiments, however, other suitableN_(col), N_(row), and N_(rot) parameters different from thecorresponding parameters defined by a legacy communication protocol areutilized.

In an embodiment, the parameters N_(col), N_(row), and N_(rot) used foran OFDM symbol being generated for an 80 MHz-wide channel with 1024point IDFT, new (e.g., not previously defined in the IEEE 802.11acStandard) N_(col), N_(row), and N_(rot) parameters are utilized. In anembodiment, the new N_(col), N_(row), and N_(rot) parameters are scaledversions of the corresponding parameters defined for an 80 MHz-widechannel in the IEEE 802.11ac Standard, in an embodiment. As an example,in an example embodiment, the new N_(col), N_(row), and N_(rot)parameters correspond to N_(col), N_(row) and N_(rot) defined for an 80MHz bandwidth by the IEEE 802.11ac Standard and scaled by a factor thatis proportional to the reduction in tone spacing with respect to theIEEE 802.11ac Standard. For example, in an illustrative embodiment, thenew N_(col) and N_(row) parameters correspond to the N_(col) and N_(row)parameters, respectively, defined for an 80 MHz bandwidth in the IEEE802.11ac Standard scaled at least approximately by sqrt(N), where sqrt () is a square root function and N is the factor by which the tonespacing is reduced for an 80 MHz bandwidth in the first communicationprotocol. Further, in an embodiment, one or both of N_(col) and N_(row)are adjusted such a product of N_(col) and N_(row) corresponds to anumber of data tones in the 80 MHz bandwidth, in an embodiment.Referring now to the N_(rot) parameter, N_(rot) corresponds to theN_(rot) parameter defined for an 80 MHz bandwidth by the IEEE 802.11acStandard scaled by N, in an example embodiment. Thus, for example, in anembodiment in which ¼ tone spacing is utilized for an 80 MHz channel,the N_(col), N_(row), and N_(rot) used by the BCC interleavers 520 areN_(col)=55 (approximately 26*2), N_(row)=18*N_(BPSCS) (2*9*N_(BPSCS)),where N_(BPSCS) is the number of coded bits per single carrier for eachspatial stream (based on modulation and coding scheme (MCS) beingutilized), and N_(rot)=58*4 if the number of spatial streams (N_(ss)) isless than or equal to 4, or N_(rot)=28*4 if the number of spatialstreams (N_(ss)) is greater than 4, in an embodiment. As anotherexample, in another embodiment, N_(rot)=62*4 if the number of spatialstreams (N_(ss)) is less than or equal to 4, or N_(rot)=30*4 or 32*4 ifthe number of spatial streams (N_(ss)) is greater than 4. In otherembodiments, however, other suitable N_(col), N_(row), and N_(rot)parameters different from the corresponding parameters defined by alegacy communication protocol are utilized.

In an embodiment in which multiple segments of coded bits correspondingto different frequency sub-bands of the 80 MHz communication channel areoperated on by respective multiple BCC interleavers 520, the parametersN_(col), N_(row), and N_(rot) used by the two BCC interleavers 318correspond to the N_(col), N_(row), and N_(rot) parameters defined bythe first communication protocol for the channel corresponding to thesub-band. As just an example, in an embodiment in which four segments ofcoded bits corresponding to respective 20 MHz sub-bands of the 80MHz-wide channel are operated on by four BCC interleavers 318, theparameters N_(col), N_(row), and N_(rot) used by the four BCCinterleavers 318 correspond to N_(col), N_(row), and N_(rot),parameters, respectively, used for a 20 MHz channel of the firstcommunication protocol (e.g., N_(col), N_(row), and N_(rot) parametersdefined for an 80 MHz communication channel by the IEEE 802.11acStandard), in an embodiment.

In an embodiment in which two segments of coded bits for a 160 MHzcommunication channel are operated on by two BCC interleavers 520, theparameters N_(col), N_(row), and N_(rot) used by the two BCCinterleavers 520 correspond to N_(col), N_(row), and N_(rot),respectively, used for an 80 MHz communication channel as defined in thefirst communication protocol (e.g., the N_(col), N_(row), and N_(rot)parameters for an 80 MHz communication channel of the firstcommunication protocol defined as described above), in an embodiment. Onthe other hand, in an embodiment in which an OFDM symbol for a 160 MHzchannel is generated using a single segment of coded bits (e.g., thesegment parsers 518 are bypassed), new (e.g., not previously defined inthe IEEE 802.11ac Standard) N_(col), N_(row), and N_(rot) parametersdefined for a 160 MHz channel by the first communication protocol areutilized.

In an embodiment in which the interleavers 520 operate on resource unitswithin an OFDMA data unit, such as the OFDMA data unit 250 of FIG. 2B,the interleavers 520 use interleaving parameters that depend on thenumber of OFDM tones in a resource unit within the OFDMA data unit.Table 1 illustrates interleaver parameters used by the interleavers 520for several RU sizes within the data unit 250 of FIG. 2B, in someembodiments.

TABLE 1 RU (number of tones) Ncol Nrot 26 8 2 (Nss ≦4) 52 16 K 106 17 29(Nss ≦4) 13 (Nss >4) 242 56 58 (Nss ≦4) 28 (Nss >4)

Referring to Table 1, in several example embodiments, the value K of theparameter N_(rot) used with a resource unit having 52 tones for Nss≦4 isone of K=11, K=13, or K=9, depending on the embodiment. Referring stillto Table 1, the value K of the parameter N_(rot) used with a resourceunit having 52 tones for Nss>4 is one of K=5, K=6, or K=7, depending onthe embodiment. In other embodiments, the value K of the parameterN_(rot) used with a resource unit having 52 tones are other suitablevalues.

In some embodiments, for example when LDPC encoding is utilized (e.g.,when the FEC encoders 312 are LDPC encoders), the BCC interleavers 520are bypassed or omitted.

With continued reference to FIG. 5, outputs of the BCC interleavers 520(or outputs of the segment parsers 518 if the BCC interleavers 520 arebypassed or omitted) are provided to constellation mappers 522. In anembodiment, each constellation mapper 522 maps a sequence of bits toconstellation points corresponding to different subcarriers/tones of anOFDM symbol. More specifically, for each spatial stream and eachsegment, a constellation mapper 522 translates every bit sequence oflength log₂(M) into one of M constellation points, in an embodiment. Theconstellation mapper 522 handles different numbers of constellationpoints depending on the MCS being utilized.

In an embodiment, the constellation mapper 522 is a quadrature amplitudemodulation (QAM) mapper that handles M=2, 4, 16, 64, 256, and 1024. Inother embodiments, the constellation mapper 522 handles differentmodulation schemes corresponding to M equaling different subsets of atleast two values from the set {2, 4, 16, 64, 256, 1024}.

In an embodiment, when LDPC encoding is utilized, the outputs of theconstellation mappers 522 are operated on by LDPC tone mappers 526. Insome embodiments, when BCC encoding is utilized (e.g., when the FECencoders 512 are BCC encoders), the LDPC tone mappers 526 are bypassedor omitted.

Each LDPC tone mapper 526 reorders constellation points corresponding toa spatial stream and a segment according to a tone remapping function.The tone remapping function is generally defined such that consecutivecoded bits or blocks of information bits are mapped onto nonconsecutivetones in the OFDM symbol to facilitate data recovery at the receiver incases in which consecutive OFDM tones are adversely affected duringtransmission. LDPC tone mapper parameters (e.g., “tone mapping distance”or the distance between two OFDM tones onto which adjacent constellationpoints are mapped) may be different in different embodiments. In anembodiment, the tone mapping distance used by the LDPC tone mapper 526for an OFDM symbol being generated for a 20 MHz channel corresponds tothe tone mapping distance defined by the IEEE 802.11ac Standard for an80 MHz channel.

In an embodiment in which multiple segments of constellation pointscorresponding to multiple sub-bands of a channel are operated on bymultiple LDPC tone mappers 526, the tone mapping distance used by eachof the operating LDPC tone mappers 526 corresponds to the tone mappingdistance defined by the first communication protocol for a channelcorresponding to each of the sub-bands. Thus, for example, each LDPCencoder 526 operating on a 20 MHz sub-band of a 40 MHz bandwidth, an 80MHz bandwidth or a 160 MHz bandwidth utilizes the tone mapping distancedefined by the first communication protocol a 20 MHz-wide channel, in anembodiment. In an embodiment, new tone mapping distances, not previouslydefined by a legacy communication protocol, are defined at least fornumbers of OFDM tones that are greater than numbers of OFDM tones usedin a legacy communication protocol. For example, in an embodiment, atone mapping distance D₁ defined for a particular bandwidth by the firstcommunication protocol is a scaled version of corresponding tone mappingdistance D₂ defined for the first bandwidth by a legacy communicationprotocol (e.g., the IEEE 802.11ac Standard). For example, D₁ is at leastapproximately to N*D₂, where N is the tone spacing reduction factor, inan embodiment.

In an embodiment in which the LDPC tone mappers 526 operate onsub-channel blocks corresponding to an OFDMA data unit, such as theOFDMA data unit 250 of FIG. 2B, the LPPC tone mappers 526 use a tonemapping distance D that depends on a size (e.g, number of OFDM tones) ofa resource unit within the OFDMA data unit. Further, in someembodiments, tone mapping is not implemented (e.g., the LDPC tonemappers 526 are bypassed or omitted) for some resource unit sizes, insome embodiment.

In an embodiment, a 26-tone RU includes 24 data tones and 2 pilot tones.In other embodiments, a 26-tone RU includes other suitable numbers ofdata tones and pilot tones. In an embodiment, tone mapping is notimplemented for a 26-tone RU, in an embodiment. In another embodiment,tone mapping is not implemented for a 26-tone RU for Nss≦4, and tonemapping is implemented for a 26-tone RU for Nss>4, with a tone mappingdistance selected from a set {4, 6, 8}, depending on the embodiment. Inanother embodiment, another suitable tone mapping distance D for a26-tone RU for Nss>4 is used.

In an embodiment, a 52-tone RU includes 48 data tones and 4 pilot tones.In other embodiments, a 52-tone RU includes other suitable numbers ofdata tones and pilot tones. In an embodiment, tone mapping is notimplemented for a 52-tone RU. In another embodiment, tone mapping is notimplemented for a 52-tone RU for Nss≦4, and tone mapping is implementedfor a 52-tone RU for Nss>4, with a tone mapping distance D selected froma set {6, 8, 12}, depending on an embodiment. In another embodiment,another suitable tone mapping distance D for a 52-tone RU for Nss>4mapping distance D is used. In some embodiments, tone mapping isimplemented for a 52-tone RU regardless of the number of spatial orspace-time streams Nss being used. In some embodiments in which tonemapping is implemented for a 52-tone RU regardless of the number ofspatial or space-time streams Nss being used, tone mapping distance D isselected from a set {6, 8, 12}. In another embodiment in which tonemapping is implemented for a 52-tone RU regardless of the number ofspatial or space-time streams Nss being used, another suitable tonemapping distance D is used.

In an embodiment, a 106-tone RU includes 102 data tones and 4 pilottones. In other embodiments, a 106-tone RU includes other suitablenumbers of data tones and pilot tones. In an embodiment, tone mapping isnot implemented for a 106-tone RU. In another embodiment, tone mappingis not implemented for a 106-tone RU for Nss≦4, and tone mapping isimplemented for a 106-tone RU for Nss>4, with a tone mapping distance Dselected from a set {6, 17, 34}, depending on an embodiment. In anotherembodiment, another suitable tone mapping distance D for a 106-tone RUfor Nss>4 mapping distance D is used. In some embodiments, tone mappingis implemented is implemented for a 106-tone RU regardless of the numberof spatial or space-time streams Nss being used.

In some embodiments in which tone mapping is implemented for a 106-toneRU regardless of the number of spatial or space-time streams Nss beingused, tone mapping distance D for a 106-tone RU is selected from a set{6, 17, 34}. In another embodiment in which tone mapping is implementedfor a 106-tone RU regardless of the number of spatial or space-timestreams Nss being used, another suitable tone mapping distance D isused.

In an embodiment, a 242-tone RU includes 234 data tones and 8 pilottones. In other embodiments, a 242-tone RU includes other suitablenumbers of data tones and pilot tones. In an embodiment, tone mapping isimplemented for a 242-tone RU regardless of the number of spatial orspace-time streams Nss being used, with tone spacing distance Dcorresponding to the tone spacing distance D defined for an 80 MHzbandwidth by the IEEE 802.11ac Standard (i.e., D=9). In otherembodiments, tone mapping is implemented for a 242-tone RU regardless ofthe number of spatial or space-time streams Nss being used, with tonespacing distance D selected from a set {18, 26, 36, 39, 52, 78}. Inanother embodiment in which tone mapping is implemented for a 242-toneRU regardless of the number of spatial or space-time streams Nss beingused, another suitable tone mapping distance D is used.

In an embodiment, a 484-tone RU includes 468 data tones and 16 pilottones. In other embodiments, a 484-tone RU includes other suitablenumbers of data tones and pilot tones. In an embodiment, tone mapping isimplemented for a 484-tone RU regardless of the number of spatial orspace-time streams Nss being used. In an embodiment, the 484 tones aregenerated using two segments, with tone spacing distance D correspondingto the tone spacing distance D defined for an 80 MHz bandwidth by theIEEE 802.11ac Standard (i.e., D=9) used in each of the segments. Inanother embodiment, the 484 tones are generated using a single segment.In some such embodiments, tone mapping is implemented regardless of thenumber of spatial or space-time streams Nss being used, with a tonemapping distance D selected from a set {9, 18, 26, 36, 39, 52, 78}. Inanother embodiment in which tone the 484 tones are generated as a singlesegment, another suitable tone mapping distance D is used.

In an embodiment, a 996-tone RU includes 980 data tones and 16 pilottones. In other embodiments, a 996-tone RU includes other suitablenumbers of data tones and pilot tones. Tone mapping is implemented for a996-tone RU regardless of the number of spatial or space-time streamsNss being used, with a tone mapping distance D selected from a set {35,49, 70, 98}, in various embodiments. In another embodiment, anothersuitable tone mapping distance D is used.

Outputs of LDPC tone mappers 526 corresponding to respective spatialstream (or, if the LDPC tone mappers 526 are bypassed or omitted,outputs of constellation mappers 522 corresponding to respective spatialstreams) are provided to respective segment deparsers 528. Each segmentdeparser 528 merges the outputs of the LDPC tone mappers 526 (or theconstellation mappers 522 if the LDPC tone mappers 526 are bypassed oromitted) corresponding to a spatial stream.

The space-time block coding (STBC) unit 530 receives the constellationpoints corresponding to the one or more spatial streams and spreads thespatial streams to a number (N_(STS)) of space-time streams. In someembodiments, the STBC unit 530 is omitted. Cyclic shift diversity (CSD)units 532 are coupled to the STBC unit 530. The CSD units 532 insertcyclic shifts into all but one of the space-time streams (if more thanone space-time stream) to prevent unintentional beamforming. For ease ofexplanation, the inputs to the CSD units 532 are referred to asspace-time streams even in embodiments in which the STBC unit 530 isomitted.

The spatial mapping unit 536 maps the N_(STS) space-time streams toN_(TX) transmit chains. In various embodiments, spatial mapping includesone or more of: 1) direct mapping, in which constellation points fromeach space-time stream are mapped directly onto transmit chains (i.e.,one-to-one mapping); 2) spatial expansion, in which vectors ofconstellation points from all space-time streams are expanded via matrixmultiplication to produce inputs to the transmit chains; and 3)beamforming, in which each vector of constellation points from all ofthe space-time streams is multiplied by a matrix of steering vectors toproduce inputs to the transmit chains. Each output of the spatialmapping unit 536 corresponds to a transmit chain, and each output of thespatial mapping unit 536 is operated on by an IDFT calculation unit 540(e.g., an inverse fast Fourier transform (IFFT) calculation unit) thatconverts a block of constellation points to a time-domain signal. In anembodiment in which the PHY processing unit 500 includes multipleprocessing paths 501 corresponding to multiple receivers of an OFDMAdata unit, each IDFT calculation unit 540 includes multiple inputscorresponding to outputs of the multiple processing paths 501. In thisembodiment, each IDFT calculation unit 540 jointly performs IDFT for allof the receivers on the OFDMA data unit.

Outputs of the IDFT units 540 are provided to GI insertion and windowingunits 544 that prepend to OFDM symbols, a guard interval (GI) portion,which is a circular extension of an OFDM symbol in an embodiment, andsmooth the edges of OFDM symbols to increase spectral delay. Outputs ofthe GI insertion and windowing units 544 are provided to analog andradio frequency (RF) units 548 that convert the signals to analogsignals and upconvert the signals to RF frequencies for transmission.The signals are transmitted in a 20 MHz, a 40 MHz, an 80 MHz, or a 160MHz bandwidth channel (e.g., corresponding to a 256-, 512-, 1024-, or2048-point IDFT at unit 540, respectively, in an embodiment, andutilizing a clock rate that is constant regardless of IDFT size), invarious embodiments and/or scenarios. In other embodiments, othersuitable channel bandwidths (and/or IDFT sizes) are utilized.

In various embodiments, the PHY processing unit 500 includes varioussuitable numbers of transmit chains (e.g., 1, 2, 3, 4, 5, 6, 7, etc.).Further, in some scenarios, the PHY processing unit 500 does not utilizeall transmit chains. As merely an illustrative example, in an embodimentin which the PHY processing unit 500 includes four transmit chains, thePHY processing unit 500 may utilize only two transmit chains or onlythree transmit chains, for example, if only two spatial streams arebeing utilized.

In the PHY processing unit 500, each transmit chain is configured togenerate a transmit signal that spans the entire communication channel(e.g., spanning 20 MHz, 40 MHz, 80 MHz, 160 MHz, etc.). In otherembodiments, however, the network interface device (e.g., networkinterface device 16 and/or network interface device 27) includesmultiple radio frequency (RF) portions corresponding to differentportions of the communication channel. For example, multiple portionsare used For instance, as merely an illustrative example, the networkinterface device includes a first RF portion corresponding to first 20MHz-wide portion of a 40 MHz-wide communication channel, and a second RFportion corresponding to second 20 MHz-wide portion of the 20 MHz-widecommunication channel. As just another example, in another embodiment,the network interface device includes a first RF portion correspondingto first 80 MHz-wide portion of a 160 MHz-wide communication channel,and a second RF portion corresponding to second 80 MHz-wide portion ofthe 160 MHz-wide communication channel.

FIG. 6 is a block diagram of a transmit portion of an example PHYprocessing unit 600 configured to generate data units, such as the dataunit 200 of FIG. 2A or the data unit 250 of FIG. 2B, that conform to thefirst communication protocol, according to an embodiment. Referring toFIG. 1, the PHY processing unit 20 of AP 14 and the PHY processing unit29 of client station 25-1 are each similar to or the same as PHYprocessing unit 600, in one embodiment. The PHY processing unit 600 issimilar to the PHY processing unit 500 of FIG. 5 and includes many ofthe same elements of the PHY processing unit 500. At least some oflike-numbered elements with the PHY processing unit 500 are notdiscussed in detail merely for purposes of brevity.

The PHY processing unit 600 includes a respective processing unit 508corresponding to each segment of multiple segments generated to by thesegment parsers 402 and, accordingly, corresponding to each frequencysub-band of the communication channel, in an embodiment. For example, afirst processing unit 508 corresponds to a first frequency sub-band ofthe communication channel, and a second processing unit corresponds to asecond frequency sub-band of the communication channel. Additionally,the PHY processing 600 does not utilize a segment deparser.

As just an example, in a transmission mode corresponding to acommunication channel having a width of 40 MHz, the first processingunit 602 a may correspond to a first 20 MHz frequency sub-band and thesecond processing unit 602 b may correspond to a second 20 MHz frequencysub-band of the communication channel. As just another example, in atransmission mode corresponding to a communication channel having awidth of 160 MHz, the first processing unit 602 a may correspond to afirst 80 MHz frequency sub-band and the second processing unit 602 b maycorrespond to a second 80 MHz frequency sub-band of the communicationchannel. In some embodiments and/or scenarios, the first frequencysub-band is contiguous with the second frequency sub-band. In otherembodiments and/or scenarios, however, the first frequency sub-band isnot contiguous with the second frequency sub-band. For example, theremay be a gap in frequency between the first frequency sub-band and thesecond frequency sub-band, and the communication channel has acumulative bandwidth equal to a sum of the bandwidth of the firstfrequency sub-band and the bandwidth of the second frequency sub-band,in an embodiment.

The first processing unit 602 a includes a respective BCC interleaver520 (if BCC interleavers 520 are not omitted), a respectiveconstellation mapper 522 and a respective LDPC tone mapper 526 (if LDPCtone mappers 526 are not omitted) for each spatial stream. The firstprocessing unit 508 a further includes the STBC unit 530, the CSD units532 and the spatial mapping unit 526. Referring to the outputs of thespatial mapping unit 536, each modulation data output of the spatialmapping unit 536 of the first processing unit 508 a corresponds to arespective transmit channel, and also corresponds to single portion ofthe communication channel. As merely an illustrative example, in anembodiment and/or transmission mode in which a 160 MHz communicationchannel is to be utilized, a modulation data output provided to a firsttransmit chain corresponding to each spatial stream corresponds to afirst 80 MHz portion of the 160 MHz communication channel. Continuingwith the illustrative example above, in an embodiment, a modulation dataoutput provided to a second transmit chain corresponding to each spatialstream corresponds to a second 80 MHz portion of the 160 MHzcommunication channel.

The block of constellation points operated on by each IDFT calculationunit 540 corresponds to all of the subcarriers corresponding to therespective portion of the communication channel. Thus, in an exampleembodiment and/or transmission mode in which a 160 MHz communicationchannel is to be utilized, each IDFT calculation unit 540 implements a1024-point IDFT corresponding to 1024 subcarriers of an 80 MHz bandwidthportion of the communication channel. The signals output by each block548 span only the respective bandwidth portion of the communicationchannel (e.g., a respective 80 MHz-wide portion of a 160 MHz-widecommunication channel), in an embodiment.

FIGS. 7-9 are diagrams of tone maps corresponding to OFDM symbols thatare generated according to the first communication protocol, in someembodiments. The PHY unit 200 (FIG. 3) is configured, in someembodiments, to generate OFDM symbols such as one of the OFDM symbols ofFIGS. 7-9, or another suitable OFDM symbol. In some embodiments, PHYunit 200 (FIG. 3) is configured to generate different OFDM symbols, suchas the OFDM symbols of FIGS. 7-9, or other suitable OFDM symbols,depending on channel conditions, the capabilities of the receive deviceto which the OFDM symbol is being transmitted, etc.

FIG. 7 is a diagram of a tone map for an OFDM symbol 700 correspondingto a 20 MHz-wide channel, according to an embodiment. The OFDM symbol700 includes 256 OFDM tones with a tone spacing that is reduced by afactor of 4 (¼ tine spacing) as compared to tone spacing defined by theIEEE 802.11ac Standard, in an embodiment. The OFDM symbol 700 has thesame format as specified for an 80 MHz communication channel in the IEEE802.11ac Standard.

The 256 tones of the OFDM symbol 700 are indexed from −128 to +127, inan embodiment. The 256 tones include 11 guard tones, three directcurrent (DC) tone, data tones, and pilot tones. The six lowest frequencytones and the five highest frequency tones are guard tones, which areprovided for filter ramp up and ramp down, in an embodiment. In anembodiment, the number of guard tones included in an OFDM symbolconforming to the first communication protocol is scaled with respect tothe number of guard tones defined for the corresponding bandwidth by theIEEE 802.11ac Standard so as to maintain at least substantially samefrequency guard band as the corresponding guard band defined by the IEEE802.11ac Standard. For example, the number of guard tones at each bandedge of an OFDM symbol conforming to the first communication protocolcorresponds to the number of guard tones defined by the IEEE 802.11acStandard scaled by

In another embodiment, the number of guard tones included in the OFDMsymbol 700 is greater than the number of guard tones defined for an 80MHz bandwidth by the IEEE 802.11ac Standard. For example, the number ofguard tones in the OFDM symbol is scaled with respect to the number ofguard tones defined by IEEE 802.11ac Standard by the scaling factor Nwhen the tone spacing is reduced by a factor of 1/N with respect to theIEEE 802.11ac Standard. Thus, for example, for an OFDM symbol with ¼tone spacing as compared to the tone spacing defined by the IEEE802.11ac Standard, the number of guard tones at a band edge of the OFDMsymbol corresponds to the number of guard tones at the correspondingband edge defined by the IEEE 802.11ac Standard multiplied by 4, in anembodiment. Accordingly, in this embodiment, the number of guard tonesat the lower and upper band edges corresponds to [6, 5]*4. In anotherembodiment, the number of guard tones at each band edge is scaled by afactor that is less than N. For example, more stringent filtering isused to transmit/receive OFDM symbols conforming to the firstcommunication protocol as compared to filtering used transmit/receiveOFDM symbols conforming to the IEEE 802.11ac Standard, in someembodiments. Generally speaking, the number of guard tones in an OFDMsymbol conforming to the first communication protocol is less than orequal to [6, 5]*N, in various embodiments. As a more specific example,the number of guard tones at the left band edge (N_(G left)) of an OFDMsymbol conforming to the first communication protocol is within therange 2≦N_(G left)≦6*N, and the number of guard tones at the right bandedge (N_(G right)) of an OFDM symbol conforming to the firstcommunication protocol is within the range 3≦N_(G right)≦5*N. Further,in an embodiment, the number of guard tones N_(G left) and N_(G right)in an OFDM symbol that conforms to the first communication protocol issuch that the condition N_(G right)=N_(G left)+1 is satisfied.

Referring again to FIG. 7, the index −1, 0, and +1 tones in the OFDMsymbol 700 are DC tones, which are provided for mitigating radiofrequency interference. In the embodiment of FIG. 7, the number of DCtones (i.e., 3 DC tones) included in the OFDM symbol 700 corresponds tothe number of DC tones defined for a 20 MHz channel by the IEEE 802.11acStandard. In an embodiment, due to the smaller tone spacing in the OFDMsymbol 700 as compared to tone spacing defined by the IEEE 802.11acStandard, the first communication protocol defines a maximum tolerabletransmitter-receiver (Tx-Rx) frequency offset that is less than thetolerable Tx-Rx frequency offset defined in the IEEE 802.11ac Standard.For example, whereas the maximum tolerable Tx-Rx frequency offsetdefined by the IEEE 802.11ac Standard is ±40 parts per million (ppm),the first communication protocol defines a smaller maximum tolerableTx-Rx frequency offset such as ±20 parts per million (ppm), for example.Additionally or alternatively, the OFDM symbol 700 includes a number ofDC tones that is greater than three DC tones, in some embodiments. Forexample, in an embodiment, the OFDM symbol 700 includes five DC tone. Inother embodiments, the OFDM symbol 700 includes other suitable numbersof DC tones (e.g., 1, 7, 9, 11, etc.). Greater number of DC tones (e.g.,5 DC tones) allows the first communication protocol to maintain themaximum tolerable Tx-Rx frequency offset requirement at leastsubstantially the same as defined by the IEEE 802.11ac Standard (i.e.,+/−40 parts per million (ppm)) while utilizing the reduced tone spacing,such as ¼ tone spacing, in the OFDM symbol 700.

With continued reference to FIG. 7, ±100, the OFDM symbol 700 includes10 pilot tones at tone indices {±117, ±89, ±75, ±39, ±11}, in theillustrated embodiment. In an embodiment, the pilot tones are used forfrequency offset estimation, for example. The number and locations ofpilot tones of the OFDM 700 corresponds to the number and locations ofpilot tones defined for an 80 MHz bandwidth by the IEEE 802.11acStandard, in this embodiment. In another embodiment, the number of pilottones in an OFDM symbol conforming to the first communication protocolcorresponds to the number of pilot defined for a corresponding bandwidthin the IEEE 802.11ac Standard. Accordingly, in an embodiment, althoughan OFDM symbol corresponding to a particular bandwidth and conforming tothe first communication protocol includes a greater number of OFDM tonesas compared to an OFDM symbol corresponding to the particular bandwidthand conforming to the IEEE 802.11ac Standard, the OFDM symbol conformingto the first communication protocol includes the same number of pilottones as the OFDM symbol corresponding to the same bandwidth andconforming to the IEEE 802.11ac Standard. In an embodiment, thelocations of the pilot tones correspond to the pilot tone locationsdefined for the corresponding bandwidth in the IEEE 802.11ac Standardscaled by the scaling factor N when the tone spacing is reduced by afactor of 1/N with respect to the IEEE 802.11ac Standard. As just anexample, the OFDM symbol 700, which correspond to a 20 MHz-wide channeland conforms to the first communication protocol with ¼ tone spacing,includes four pilot tones located at indices {±28, ±84}, in anotherembodiment. As just another example, an OFDM symbol that corresponds toa 40 MHz-wide channel and conforms to the first communication protocolwith ¼ tone spacing includes 512 OFDM tones, of which six tones, locatedat indices {±44, ±100, ±212}, are pilot tones, in an embodiment.

Referring still to FIG. 7, the OFDM tones in the tone map 700 that arenot used as DC tones, guard tones, or pilot tones as used as data tones,in an embodiment. In some embodiments, the number of OFDM tones used asdata tones is selected such that the number of data tones is divisibleby 3 and 6. In such embodiments, the OFDM symbol includes an integernumber of data bits per OFDM symbol (N_(DBPS)) for all or mostmodulation and coding schemes defined by the first communicationprotocol. The integer N_(DBPS) is required or desired when BCC encodingis used to encode the data bits, in an embodiment. On the other hand,when LDPC encoding is used, an integer N_(DBPS) is not needed, and anysuitable number of OFDM tones can be used as data tones, in anembodiment.

In some embodiment, the first communication protocol excludes MCSs thatdo not lead to an integer N_(DBPS) from consideration, at least when BCCencoding is being utilized. In another embodiment, the firstcommunication protocol utilizes a suitable technique that allows anon-integer N_(DBPS) to be encoded using one or more BCC encoders orusing an LDPC encoder. Some example techniques used in some embodimentsfor encoding non-integer N_(DBPS) using one or more BCC encoders isdescribed, for example, in U.S. patent application Ser. No. 13/246,577,entitled “Parsing and Encoding Methods in a Communication System,” filedSep. 27, 2011, which is hereby incorporated by reference in itsentirety. Some example techniques used in some embodiments for encodingnon-integer N_(DBPS) using an LDPC encoder is described, for example, inU.S. patent application Ser. No. 13/439,623, entitled “Data EncodingMethods in a Communication System,” filed Apr. 4, 2012, which is herebyincorporated by reference in its entirety. In an embodiment, BCCencoding is not used in the first communication protocol, and only LDPCencoding in allowed.

FIG. 8 is a diagram of a tone map for an OFDM symbol 800 correspondingto a 40 MHz-wide channel, according to an embodiment. The OFDM symbol800 includes 512 tones indexed from −256 to +255, in an embodiment. The512 tones include guard tones, DC tones, data tones, and pilot tones.The 12 lowest frequency tones and the 11 highest frequency tones areguard tones. The three tones indexed from −1 to +1 are DC tones. TheOFDM symbol 800 includes 486 data/pilot tones, of which six tones arepilot tones as defined for a 40 MHz-wide channel by the IEEE 802.11acStandard. The pilot tone locations correspond to the pilot tonelocations defined for a 40 MHz-wide channel by the IEEE 802.11acStandard scaled by a factor of 4, in the illustrated embodiment. Inparticular, the pilot tones are located at indices {±44, ±100, ±212} inthe illustrated embodiment. The OFDM symbol 800 includes 480 data tones.Accordingly, the number of data tones is divisible by 3, 4 and 6. As aresult, an integer number of N_(DBPS) requirement is satisfied for allor most modulation and coding schemes defined by the first communicationprotocol, in an embodiment. Whereas data tone efficiency in a 40MHz-wide channel according to the IEEE 802.11ac Standard isapproximately 84.38% (108 data tones/128 total tones), data toneefficiency on the OFDM symbol 800 is approximately 93.75% (480 datatones/512 total tones), in the illustrated embodiment.

As just another example, an OFDM symbol that corresponds to an 80 MHzcorresponds to a size 512 IDFT and includes 512 tones, in an embodiment.Accordingly, the OFDM symbol utilizes ½ tone spacing with respect to thetone spacing defined by the IEEE 802.11ac Standard, in this embodiment.The 512 tones, indexed −512 to 511, include guard tones, DC tones, datatones, and pilot tones. 11 lowest frequency tones and the 12 highestfrequency tones are guard tones. Three tones indexed from −1 to +1 areDC tones. The OFDM symbol includes eight pilot tones, as defined for an80 MHz-wide channel by the IEEE 802.11ac Standard. The pilot tonelocations correspond to the pilot tone locations defined for an 80MHz-wide channel by the IEEE 802.11ac Standard scaled by a factor of 2,in an embodiment. In particular, the pilot tones are located at indices{±22, ±78, ±150, ±206}, in an embodiment. The OFDM symbol includes 480data tones. Whereas data tone efficiency in an 80 MHz-wide channelaccording to the IEEE 802.11ac Standard is approximately 91.41% (234data tones/256 total tones), data tone efficiency on the thatcorresponds to an 80 MHz corresponds to a size 512 IDFT and includes 512tones is approximately 93.75% (480 data tones/512 total tones), in anembodiment.

FIG. 9 is a diagram of a tone map for an OFDM symbol 900 correspondingto an 80 MHz-wide channel, according to an embodiment. The OFDM symbol900 includes 1024 tones indexed from −512 to +511, in an embodiment. The1024 tones include guard tones, DC tones, data tones, and pilot tones.The 12 lowest frequency tones and the 11 highest frequency tones areguard tones. The three tones indexed from −1 to +1 are DC tones. TheOFDM symbol 900 includes 998 data/pilot tones, of which eight tones arepilot tones as defined for an 80 MHz-wide channel by the IEEE 802.11acStandard. The pilot tone locations correspond to the pilot tonelocations defined for an 80 MHz-wide channel by the IEEE 802.11acStandard scaled by a factor of 4, in the illustrated embodiment. Inparticular, the pilot tones are located at indices {±44, ±156, ±300,±412}, in the illustrated embodiment. The OFDM symbol 900 includes 990data tones. Accordingly, the number of data tones is divisible by 3 and6, in this embodiment. As a result, an integer number of N_(DBPS)requirement is satisfied for all or most modulation and coding schemesdefined by the first communication protocol, in an embodiment. Whereasdata tone efficiency in an 80 MHz-wide channel according to the IEEE802.11ac Standard is approximately 91.41% (234 data tones/256 totaltones), data tone efficiency on the OFDM symbol 900 is approximately96.68% (990 data tones/1024 total tones), in the illustrated embodiment.

In some embodiments, an OFDM symbol for a 40 MHz channel corresponds totwo concatenated 20 MHz OFDM symbols. For example, an OFDM symbol for a40 MHz-wide channel, according to an embodiment, corresponds to a size512 IDFT (or two 128 IDFTs). The OFDM symbol for a 40 MHz-wide channelcorresponds to two concatenated 20 MHz OFDM symbols 700 of FIG. 7, in anembodiment. Similarly, an OFDM symbol for a 160 MHz-wide channelcorresponds to two concatenated 80 MHz OFDM symbols, in an exampleembodiment. For example, the OFDM symbol for a 160 MHz-wide channelcorresponds to two concatenated 80 MHz OFDM symbols 900 of FIG. 9, in anexample embodiment. Alternatively, in another embodiment, an OFDM symbolthat corresponds to a 160 MHz-wide channel is generated using a singlesegment of coded bits and a size 2048 IDFT (with an OFDM symbol thatutilizes ½ tone spacing) or a size 1024 IDFT (with an OFDM symbol thatutilizes ½ tone spacing). In an embodiment, the OFDM symbol thatcorresponds to a 160 MHz-wide channel and is generated using a singlesegment of coded bits includes guard tones, DC tones and pilot tones. Inan embodiment, an OFDM symbol that corresponds to a 160 MHz-wide channeland conforms to a single segment format of the first communicationprotocol includes less pilot tones as compared to a compound 160 MHzOFDM symbol that conforms to the IEEE 802.11ac Standard. For example, anOFDM symbol an OFDM symbol that corresponds to a 160 MHz-wide channeland conforms to a single segment format of the first communicationprotocol includes ten pilot tones that are at least approximatelyequally spaced across the 160 MHz bandwidth. In an embodiment, pilottone locations defined for a 160 MHz-wide channel by the firstcommunication protocol are divisible by 4. In another embodiment,however, pilot tone locations defined for a 160 MHz-wide channel by thefirst communication protocol are not necessarily divisible by 4.

As just an example, an OFDM symbol that corresponds to a 160 MHz-widechannel and size 2048 IDFT (¼ tone spacing) includes 2048 tones, in anembodiment. The 2048 tones, indexed −1024 to 1023, include guard tones,DC tones, data tones, and pilot tones. 13 lowest frequency tones and the12 highest frequency tones are guard tones. Three tones indexed from −1to +1 are DC tones. The 2048 tones further include 10 pilot tones, in anembodiment. The 10 pilot tones are at least approximately equally spacedover the 160 MHz bandwidth, in an embodiment. In an embodiment, pilottone locations of the 10 pilot tones are divisible by 4. In anotherembodiment, however, pilot tone locations of the 10 pilot tones are notnecessarily divisible by 4. The 2048 tones include 2010 data tones, inan embodiment. The number of data tones is divisible by 3 and 6, in thisembodiment. Data tone efficiency is approximately 98.14% (2010 datatones/1048 total tones), in this embodiment.

FIG. 10 is a diagram of a PHY data unit 1000 that the AP 14 isconfigured to transmit to a client station (e.g., the client stations25-1) via OFDM modulation, according to an embodiment. In an embodiment,the client station 25-1 is also configured to transmit the data unit1000 to the AP 14. In an embodiment, PHY processing units such as thePHY processing unit 500 of FIG. 5 or the PHY processing unit 600 of FIG.6 are configured to generate the data unit 1000. In other embodiments,however, the data unit 1000 is generated by a PHY processing unitdifferent from the PHY processing unit 500 of FIG. 5 or the PHYprocessing unit 600 of FIG. 6.

The OFDM data unit 1000 is similar to the OFDM data unit 200 of FIG. 2Aand includes many of the same elements of the OFDM data unit 200 of FIG.2A. At least some of like-numbered elements with the OFDM data unit 200of FIG. 2A are not discussed in detail merely for purposes of brevity.Additionally, the OFDM data unit 1000 includes a signal extension (SE)field 1002. The SE field 1002 follows the data field 204, in theillustrated embodiment. In an embodiment, the SE field 1002 is providesextra time that a receiver of the data unit 1000 may use decode an endof the data unit 1000 before transmitting an acknowledgement toacknowledge successful (or unsuccessful) receipt of the data unit 1000.For example, according to the first communication, the receiving devicetransmits the acknowledgement signal after a certain time period, suchas a short interframe space (SIFS) of 16 μs, in an embodiment. However,due to reduced tone spacing and higher data efficiency of the firstcommunication protocol, the receiving device needs to process and decodea relatively larger number of bits in each OFDM symbol of the data field240 of the data unit 1000, particularly when the data unit 1000 istransmitted in a transmission mode corresponding to a relatively largerbandwidth (e.g., 80 MHz, 160 MHz, etc.) and/or using a modulation andcoding scheme (MCS) with relatively larger modulation order and/orrelatively high coding rate (“high order MCS”), in at least someembodiments and/or scenarios. In an embodiment, the SE field 1002 is ofa suitable length to provide a sufficiently long time to allow thereceiving device to process and decode OFDM symbols of the data portion240, and to prepare an acknowledgement frame, prior to expiration of thecertain time period (e.g., SIFS) after the end of the data unit 1000. Inan embodiment, the receiver is aware, for example a priori beforereceiving the data unit 1000, or after decoding a preamble (e.g., theHEW-SIGA field 220 and/or the HEW_SIGB field 235) of the data unit 1000,of the presence and the length of the SE field 1002 in the data unit1000. Further, a length indication in the L-SIG field 215 indicative ofa length of the data unit 1000 after the L-SIG field 215 indicates alength that includes the SE field 1002, in an embodiment. The receivingdevice, however, need not process and/or decode the SE field 1002, in anembodiment.

In an embodiment, the SE field 1002 includes a set of “zero” bits. Inanother embodiment, the SE field 1002 includes any suitable “junk” bits.In an embodiment, the junk bits of the SE field 1002 are provided tomaintain the same PAPR as in the data portion 240. In an embodiment, theSE field 1002 includes one or more OFDM symbols generating using anormal tone spacing and a regular guard interval of 0.8 μs. In thisembodiment, the duration of each of one or more OFDM symbols of the SEfield 1002 is 4 μs. In other embodiments, however, one or more OFDMsymbols of the SE field 1002 are generated with a suitable tone spacingdifferent from the normal tone spacing and/or with a guard intervaldifferent from the regular guard interval. In at least some suchembodiments, the duration of each of the one or more OFDM symbolsgenerated with a suitable tone spacing different from the normal tonespacing and/or with a guard interval different from the regular guardinterval is a value different from 4 μs. In some embodiments, a powerboost is provided for the SE field 1002 to maintain power that is thesame as or similar to the power of the data portion 240.

In an embodiment, an SE field, such as the SE field 1002, is used withdata units conforming to all transmission modes (e.g., all channelbandwidths and all modulation and coding schemes) defined by the firstcommunication protocol. Alternatively, in another embodiment, an SEfield such as the SE field 1002 is used with data units conforming toonly some transmission modes (e.g., with only some combinations ofchannel bandwidths and modulation and coding schemes) defined by thefirst communication protocol. As just an illustrative example, an SEfield such as the SE field 1002 is used only with 80 MHz-wide and 160MHz-wide channels, in an embodiment. As another example, an SE fieldsuch as the SE field 1002 is used only with 80 MHz-wide and 160 MHz-widechannels and additionally with only one or more high order modulationand coding schemes. In an embodiment, a transmitting device determineswhether or not to include an SE field in a data unit, and indicatespresence or absence of an SE field in a preamble of the data unit. Forexample, the HEW-SIGA field 220 or the HEW-SIGB field 235 of the dataunit 1000 includes an indication (e.g., a single bit) that indicatespresence or absence of an SE field in the data unit 1100, in anembodiment.

FIG. 11 is a flow diagram of an example method 1100 for generating adata unit, according to an embodiment. With reference to FIG. 1, themethod 1100 is implemented by the network interface device 16, in anembodiment. For example, in one such embodiment, the PHY processing unit20 is configured to implement the method 1100. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 1100. With continued reference to FIG. 1, inyet another embodiment, the method 1100 is implemented by the networkinterface device 27 (e.g., the PHY processing unit 29 and/or the MACprocessing unit 28). In other embodiments, the method 1100 isimplemented by other suitable network interface devices.

At block 1102, one or more OFDM symbols for a data unit conforming to afirst communication protocol are generated. Each OFDM symbol occupies afirst bandwidth, is generated with a first tone spacing, and includes aset of pilot tones, in an embodiment. In an embodiment, the first tonespacing is a reduced tone spacing with respect to a tone spacing definedfor the first bandwidth by a second communication protocol. As anexample, the first tone spacing corresponds to the reduced tone spacing350 of FIG. 3C whereas the second tone spacing corresponds to the normaltone spacing 300 of FIG. 3A. In this embodiment, the first tone spacingis reduced by a factor ¼ with respect to the second tone spacing. As aresult, an OFDM symbol generated at block 1102 includes a greater numberof tones (scaled by a factor of 4) as compared to OFDM symbols generatedfor the first bandwidth according to the second communication protocol.On the other hand, the set of pilot tones included in the OFDM symbol isthe same as the number of pilot tones defined for the first bandwidth bythe second communication protocol, in an embodiment. In an embodiment,the first communication protocol is the HEW communication protocol andthe second communication protocol is the IEEE 802.11ac Standard. Inanother embodiment, the first communication protocol and/or the secondcommunication protocol is another suitable communication protocol.

At block 1104, the data unit is generated. In an embodiment, one of thedata unit 200 of FIG. 2A or the data unit 1000 of FIG. 10 is generated.In another embodiment, another suitable data unit is generated. The dataunit is generated to include the one or more OFDM symbols generated atblock 1102, in an embodiment. The data unit is generated to include theone or more OFDM symbols generated at block 1102 in a data portion ofthe data unit, in an embodiment.

FIG. 12 is a flow diagram of an example method 1200 for generating adata unit, according to an embodiment. With reference to FIG. 1, themethod 1200 is implemented by the network interface device 16, in anembodiment. For example, in one such embodiment, the PHY processing unit20 is configured to implement the method 1200. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 1200. With continued reference to FIG. 1, inyet another embodiment, the method 1200 is implemented by the networkinterface device 27 (e.g., the PHY processing unit 29 and/or the MACprocessing unit 28). In other embodiments, the method 1200 isimplemented by other suitable network interface devices.

At block 1202, one or more OFDM symbols for a data unit are generated.Block 1202 includes blocks 1204 and 1206. At block 1204, if the dataunit is to be transmitted in a first transmission mode corresponding toa first bandwidth or in a second transmission mode corresponding to asecond bandwidth, the one or more OFDM symbols are generated based on afirst tone map corresponding to a first number of OFDM tones. In anembodiment, the second bandwidth is twice of the first bandwidth. Forexample, in an embodiment, the first bandwidth is 20 MHz and the secondbandwidth is 40 MHz. In other embodiments, the first bandwidth is asuitable bandwidth different from 20 MHz and/or the second bandwidth isa suitable bandwidth different from 40 MHz. In an embodiment, the firsttone map corresponds to 256 OFDM tones (e.g., the tone map 700 of FIG. 7or another suitable tone map having 256 OFDM tones). In this embodiment,if the data unit is to be transmitted in the first transmission modecorresponding to the first bandwidth, each OFDM symbol generated atblock 1204 includes 256 OFDM tones generated based on the first tonemap. Continuing with the same embodiment, if the data unit is to betransmitted in the second transmission mode corresponding to the secondbandwidth, each OFDM symbol generated at block 1204 includes 512 OFDMtones. In particular, if the data unit is to be transmitted in thesecond transmission mode, each OFDM symbol generated at block 1204includes two blocks of 256 OFDM tones, wherein each block corresponds toa sub-band of the second bandwidths and is generated based on the firsttone map shifted or mirrored to the corresponding sub-band, in anembodiment. For example, a first block corresponds to the lower 20 MHzsub-band of the 40 MHz-wide channel and is generated based on the firsttone map shifted or mirrored to the lower 20 MHz sub-band of the 40MHz-wide channel, and a second block corresponds to the upper 20 MHzsub-band of the 40 MHz-wide channel and is generated based on the firsttone map shifted or mirrored to the upper 20 MHz sub-band of the 40MHz-wide channel, in an embodiment. In another embodiment, the firsttone map includes a suitable number of OFDM tones different from 256OFDM tones.

At block 1206, if the data unit is to be transmitted in a thirdtransmission mode corresponding to a third bandwidth or in a fourthtransmission mode corresponding to a fourth bandwidth, the one or moreOFDM symbols are generated based on a second tone map corresponding to asecond number of OFDM tones. In an embodiment, the third bandwidth istwice of the second bandwidth and the fourth bandwidth is twice of thethird bandwidth. For example, continuing with the embodiment above, ifat block 1204 the first bandwidth is 20 MHz and the second bandwidth is40 MHz, then at block 1206 the third bandwidth is 80 MHz and the fourthbandwidth is 160 MHz, in an embodiment. In other embodiments, the thirdbandwidth is a suitable bandwidth different from 80 MHz and/or thefourth bandwidth is a suitable bandwidth different from 160 MHz. In anembodiment, the second tone map corresponds to 1024 OFDM tones. In thisembodiment, if the data unit is to be transmitted in the thirdtransmission mode corresponding to the third bandwidth, each OFDM symbolgenerated at block 1206 includes 1024 OFDM tones (e.g., the tone map 900of FIG. 9 or another suitable tone map having 1024 OFDM tones).Continuing with the same embodiment, if the data unit is to betransmitted in the fourth transmission mode corresponding to the fourthbandwidth, each OFDM symbol generated at block 1206 includes 2048 OFDMtones. In particular, if the data unit is to be transmitted in thesecond transmission mode, each OFDM symbol generated at block 1206includes two blocks of 1024 OFDM tones, wherein each block correspondsto a sub-band of the fourth bandwidths and is generated based on thesecond tone map shifted or mirrored to the corresponding sub-band of thefourth bandwidths, in an embodiment. For example, a first blockcorresponds to the lower 80 MHz sub-band of the 160 MHz-wide channel andis generated based on the first tone map shifted or mirrored to thelower 80 MHz sub-band of the 160 MHz-wide channel, and a second blockcorresponds to the upper 80 MHz sub-band of the 160 MHz-wide channel andis generated based on the first tone map shifted or mirrored to theupper 80 MHz sub-band of the 160 MHz-wide channel, in an embodiment. Inanother embodiment, the second tone map includes a suitable number ofOFDM tones different from 1024 OFDM tones.

At block 1208, the data unit is generated. In an embodiment, one of thedata unit 200 of FIG. 2A or the data unit 1000 of FIG. 10 is generated.In another embodiment, another suitable data unit is generated. The dataunit is generated to include the one or more OFDM symbols generated atblock 1202, in an embodiment. The data unit is generated to include theone or more OFDM symbols generated at block 1202 in a data portion ofthe data unit, in an embodiment.

Further aspects of the present invention relate to one or more of thefollowing clauses.

In an embodiment, a method for generating a data unit for transmissionvia a communication channel, the data unit conforming to a firstcommunication protocol, includes generating, at a communication device,one or more orthogonal frequency division multiplexing (OFDM) symbols,wherein each OFDM symbol of the one or more OFDM symbols (i) occupies afirst bandwidth, (ii) is generated with a first tone spacing, and (iii)includes a set of pilot tones. The first tone spacing is a fraction 1/Nof a second tone spacing, the second tone spacing defined for the firstbandwidth by a second communication protocol, wherein N is a positiveinteger greater than one. The set of pilot tones includes a same numberof pilot tones as defined for the first bandwidth by the secondcommunication protocol. The method additionally includes generating, atthe communication device, the data unit to include the one or more OFDMsymbols in a data portion of the data unit.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

Generating the one or more OFDM symbols includes encoding informationbits using one or more binary convolution code (BCC) encoders togenerate coded bits, interleaving the coded bits using a first set ofinterleaving parameters, wherein interleaving parameters in the firstset of interleaving parameters are scaled versions of correspondinginterleaving parameters in a second set of interleaving parameters, thesecond set of interleaving parameters defined for the first bandwidth bythe second communication protocol, mapping the interleaved coded bitsonto a plurality of constellation points, and forming the one or moreOFDM symbols based on the plurality of constellation points.

The first set of interleaving parameters includes N_(col), N_(row), andN_(rot).

N_(col) of the first set of interleaving parameters is N_(col) of thesecond set of interleaving parameters multiplied by square root of N andadjusted based on a total number of data tones in each OFDM symbol.

N_(row) of the first set of interleaving parameters is N_(row) of thesecond set of interleaving parameters multiplied by square root of N.

N_(rot) of the first set of interleaving parameters is N_(rot) of thesecond set of interleaving parameters multiplied by N.

Generating the one or more OFDM symbols includes encoding informationbits using one or more low density parity check (LDPC) encoders togenerate coded bits, mapping blocks of coded bits onto constellationpoints; and mapping consecutively generated constellation points ontonon-consecutive tones using a tone mapping distance D₁, wherein the tonemapping distance D₁ is a scaled version of corresponding tone mappingdistance D₂ defined for the first bandwidth by the second communicationprotocol, wherein D₁=N*D₂.

Each OFDM symbol of the one or more OFDM symbols further includes afirst set of guard tones, and wherein the first set of guard tonesincludes a greater number of guard tones than a number of guard tones ina second set of guard tones, the second set of guard tones defined forthe first bandwidth by the second communication protocol.

The first bandwidth is 80 MHz, and wherein each OFDM symbol of the oneor more OFDM symbols includes 1024 tones.

The integer N is equal to four.

Generating the data unit further comprises generating the data unit tofurther include an extension signal field that follows the one or moreOFDM symbols, wherein the extension signal field is generated using thesecond tone spacing defined for the first bandwidth by the secondcommunication protocol.

In another embodiment, an apparatus comprises a network interface devicehaving one or more integrated circuits configured to generate one ormore orthogonal frequency division multiplexing (OFDM) symbols for adata unit that conforms to a first communication protocol, wherein eachOFDM symbol of the one or more OFDM symbols (i) occupies a firstbandwidth, (ii) are generated with a first tone spacing, and (iii)includes a set of pilot tones. The first tone spacing is a fraction 1/Nof a second tone spacing, the second tone spacing defined for the firstbandwidth by a second communication protocol, wherein N is a positiveinteger greater than one. The set of pilot tones includes a same numberof pilot tones as defined for the first bandwidth by the secondcommunication protocol. The one or more integrated circuits are furtherconfigured to generate the data unit to include the one or more OFDMsymbols in a data portion of the data unit.

In other embodiments, the apparatus includes any suitable combination ofone or more of the following features.

The one or more integrated circuits are further configured to encodeinformation bits using one or more binary convolution code (BCC)encoders to generate coded bits to be included in the data unit.

The one or more integrated circuits are further configured to interleavethe coded bits coded bits, including interleaving the coded bits using afirst set of interleaving parameters, wherein interleaving parameters inthe first set of interleaving parameters are scaled versions ofcorresponding interleaving parameters in a second set of interleavingparameters, the second set of interleaving parameters defined for thefirst bandwidth by the second communication protocol.

The one or more integrated circuits are further configured to map theinterleaved coded bits onto a plurality of constellation points, andform the one or more OFDM symbols based on the plurality ofconstellation points.

The first set of interleaving parameters includes N_(col), N_(row), andN_(rot).

N_(col) of the first set of interleaving parameters is N_(col) of thesecond set of interleaving parameters multiplied by square root of N andadjusted based on a total number of data tones in each OFDM symbol.

N_(row) of the first set of interleaving parameters is N_(row) of thesecond set of interleaving parameters multiplied by square root of N.

N_(rot) of the first set of interleaving parameters is N_(rot) of thesecond set of interleaving parameters multiplied by N.

The one or more integrated circuits are configured to encode informationbits using one or more low density parity check (LDPC) encoders togenerate coded bits.

The one or more integrated circuits are further configured to map blocksof coded bits onto constellation points.

The one or more integrated circuits are further configured to mapconsecutively generated constellation points onto non-consecutive tonessuch using a tone mapping distance D₁, wherein the tone mapping distanceD₁ is a scaled version of corresponding tone mapping distance D₂ definedfor the first bandwidth by the second communication protocol, whereinD₁=N*D₂.

The one or more integrated circuits are configured to generate each OFDMsymbol of the one or more OFDM symbols to further include a first set ofguard tones, and wherein the first set of guard tones includes a greaternumber of guard tones than a number of guard tones in a second set ofguard tones, the second set of guard tones defined for the firstbandwidth by the second communication protocol.

The first bandwidth is 80 MHz, and wherein each OFDM symbol of the oneor more OFDM tones includes 1024 tones.

The integer N is equal to four.

The one or more integrated circuits are further configured to generatethe data unit to include (i) the one or more OFDM symbols and (ii) anextension signal field that follows the one or more OFDM symbols,wherein the extension signal field is generated using the second tonespacing defined for the first bandwidth by the second communicationprotocol.

In yet another embodiment, a method for generating a data unit fortransmission via a communication channel includes generating, at acommunication device, one or more orthogonal frequency divisionmultiplexing (OFDM) symbols, including generating the one or more OFDMsymbols based on a first tone map corresponding to a first number ofOFDM tones or based on a second tone map corresponding to a secondnumber of OFDM tones. The first tone map is used if the data unit is tobe transmitted in a first transmission mode corresponding to a firstbandwidth or a second transmission mode corresponding to a secondbandwidth, wherein the second bandwidth is twice of the first bandwidth.The second tone map used if the data unit is to be transmitted in athird transmission mode corresponding to a third bandwidth or a fourthtransmission mode corresponding to a fourth bandwidth, wherein the thirdbandwidth is twice of the second bandwidth and the fourth bandwidth istwice of the third bandwidth. The method additionally includesgenerating the data unit to include the one or more OFDM symbols in adata portion of the data unit.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

The first bandwidth is 20 MHz, the second bandwidth is 40 MHz, the thirdbandwidth is 80 MHz, and the fourth bandwidth is 160 MHz.

The first number of OFDM tones is 256 tones, the second number of OFDMtones is 512 tones, the third number of OFDM tones is 1024 tones, andthe fourth number of OFDM tones is 2048 tones.

In still another embodiment, an apparatus comprises a network interfacedevice having one or more integrated circuits configured to generate oneor more orthogonal frequency division multiplexing (OFDM) symbols,including generating the one or more OFDM symbols based on a first tonemap corresponding to a first number of OFDM tones or based on a secondtone map corresponding to a second number of OFDM tones.

The first tone map is used if the data unit is to be transmitted in afirst transmission mode corresponding to a first bandwidth or a secondtransmission mode corresponding to a second bandwidth, wherein thesecond bandwidth is twice of the first bandwidth. The second tone mapused if the data unit is to be transmitted in a third transmission modecorresponding to a third bandwidth or a fourth transmission modecorresponding to a fourth bandwidth, wherein the third bandwidth istwice of the second bandwidth and the fourth bandwidth is twice of thethird bandwidth. The one or more integrated circuits are furtherconfigured to generate the data unit to include the one or more OFDMsymbols in a data portion of the data unit.

In other embodiments, the apparatus includes any suitable combination ofone or more of the following features.

The first bandwidth is 20 MHz, the second bandwidth is 40 MHz, the thirdbandwidth is 80 MHz, and the fourth bandwidth is 160 MHz.

The first number of OFDM tones is 256 tones, the second number of OFDMtones is 512 tones, the third number of OFDM tones is 1024 tones, andthe fourth number of OFDM tones is 2048 tones. At least some of thevarious blocks, operations, and techniques described above may beimplemented utilizing hardware, a processor executing firmwareinstructions, a processor executing software instructions, or anycombination thereof. When implemented utilizing a processor executingsoftware or firmware instructions, the software or firmware instructionsmay be stored in any computer readable memory such as on a magneticdisk, an optical disk, or other storage medium, in a RAM or ROM or flashmemory, processor, hard disk drive, optical disk drive, tape drive, etc.Likewise, the software or firmware instructions may be delivered to auser or a system via any known or desired delivery method including, forexample, on a computer readable disk or other transportable computerstorage mechanism or via communication media. Communication mediatypically embodies computer readable instructions, data structures,program modules or other data in a modulated data signal such as acarrier wave or other transport mechanism. The term “modulated datasignal” means a signal that has one or more of its characteristics setor changed in such a manner as to encode information in the signal. Byway of example, and not limitation, communication media includes wiredmedia such as a wired network or direct-wired connection, and wirelessmedia such as acoustic, radio frequency, infrared and other wirelessmedia. Thus, the software or firmware instructions may be delivered to auser or a system via a communication channel such as a telephone line, aDSL line, a cable television line, a fiber optics line, a wirelesscommunication channel, the Internet, etc. (which are viewed as being thesame as or interchangeable with providing such software via atransportable storage medium). The software or firmware instructions mayinclude machine readable instructions that, when executed by theprocessor, cause the processor to perform various acts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for generating a data unit fortransmission via a communication channel, the data unit conforming to afirst communication protocol, the method comprising: generating, at acommunication device, one or more orthogonal frequency divisionmultiplexing (OFDM) symbols, wherein each OFDM symbol of the one or moreOFDM symbols (i) occupies a first bandwidth, (ii) is generated with afirst tone spacing, and (iii) includes a set of pilot tones, wherein thefirst tone spacing is a fraction 1/N of a second tone spacing, thesecond tone spacing defined for the first bandwidth by a secondcommunication protocol, wherein N is a positive integer greater thanone, and the set of pilot tones includes a same number of pilot tones asdefined for the first bandwidth by the second communication protocol;and generating, at the communication device, the data unit to includethe one or more OFDM symbols in a data portion of the data unit.
 2. Themethod of claim 1, wherein generating the one or more OFDM symbolsincludes: encoding information bits using one or more binary convolutioncode (BCC) encoders to generate coded bits; interleaving the coded bitsusing a first set of interleaving parameters, wherein interleavingparameters in the first set of interleaving parameters are scaledversions of corresponding interleaving parameters in a second set ofinterleaving parameters, the second set of interleaving parametersdefined for the first bandwidth by the second communication protocol;mapping the interleaved coded bits onto a plurality of constellationpoints; and forming the one or more OFDM symbols based on the pluralityof constellation points.
 3. The method of claim 2, wherein the first setof interleaving parameters includes N_(col), N_(row), and N_(rot),wherein: N_(col) of the first set of interleaving parameters is N_(col)of the second set of interleaving parameters multiplied by square rootof N and adjusted based on a total number of data tones in each OFDMsymbol; N_(row) of the first set of interleaving parameters is N_(row)of the second set of interleaving parameters multiplied by square rootof N; and N_(rot) of the first set of interleaving parameters is N_(rot)of the second set of interleaving parameters multiplied by N.
 4. Themethod of claim 1, wherein generating the one or more OFDM symbolsincludes: encoding information bits using one or more low density paritycheck (LDPC) encoders to generate coded bits; mapping blocks of codedbits onto constellation points; and mapping consecutively generatedconstellation points onto non-consecutive tones using a tone mappingdistance D₁, wherein the tone mapping distance D₁ is a scaled version ofcorresponding tone mapping distance D₂ defined for the first bandwidthby the second communication protocol, wherein D₁=N*D₂.
 5. The method ofclaim 1, wherein each OFDM symbol of the one or more OFDM symbolsfurther includes a first set of guard tones, and wherein the first setof guard tones includes a greater number of guard tones than a number ofguard tones in a second set of guard tones, the second set of guardtones defined for the first bandwidth by the second communicationprotocol.
 6. The method of claim 1, wherein the first bandwidth is 80MHz, and wherein each OFDM symbol of the one or more OFDM symbolsincludes 1024 tones.
 7. The method of claim 1, wherein the integer N isequal to four.
 8. The method of claim 1, wherein generating the dataunit further comprises generating the data unit to further include anextension signal field that follows the one or more OFDM symbols,wherein the extension signal field is generated using the second tonespacing defined for the first bandwidth by the second communicationprotocol.
 9. An apparatus, comprising: a network interface device havingone or more integrated circuits configured to generate one or moreorthogonal frequency division multiplexing (OFDM) symbols for a dataunit that conforms to a first communication protocol, wherein each OFDMsymbol of the one or more OFDM symbols (i) occupies a first bandwidth,(ii) are generated with a first tone spacing, and (iii) includes a setof pilot tones, wherein the first tone spacing is a fraction 1/N of asecond tone spacing, the second tone spacing defined for the firstbandwidth by a second communication protocol, wherein N is a positiveinteger greater than one, and the set of pilot tones includes a samenumber of pilot tones as defined for the first bandwidth by the secondcommunication protocol, and generate the data unit to include the one ormore OFDM symbols in a data portion of the data unit.
 10. The apparatusof claim 9, wherein the one or more integrated circuits are furtherconfigured to: encode information bits using one or more binaryconvolution code (BCC) encoders to generate coded bits to be included inthe data unit; interleave the coded bits using a first set ofinterleaving parameters, wherein interleaving parameters in the firstset of interleaving parameters are scaled versions of correspondinginterleaving parameters in a second set of interleaving parameters, thesecond set of interleaving parameters defined for the first bandwidth bythe second communication protocol; map the interleaved coded bits onto aplurality of constellation points; and form the one or more OFDM symbolsbased on the plurality of constellation points.
 11. The apparatus ofclaim 10, wherein the first set of interleaving parameters includesN_(col), N_(row), and N_(rot), wherein: N_(col) of the first set ofinterleaving parameters is N_(col) of the second set of interleavingparameters multiplied by square root of N and adjusted based on a totalnumber of data tones in each OFDM symbol; N_(row) of the first set ofinterleaving parameters is N_(row) of the second set of interleavingparameters multiplied by square root of N; and N_(rot) of the first setof interleaving parameters is N_(rot) of the second set of interleavingparameters multiplied by N.
 12. The apparatus of claim 9, wherein theone or more integrated circuits are configured to: encode informationbits using one or more low density parity check (LDPC) encoders togenerate coded bits; map blocks of coded bits onto constellation points;and map consecutively generated constellation points ontonon-consecutive tones such using a tone mapping distance D₁, wherein thetone mapping distance D₁ is a scaled version of corresponding tonemapping distance D₂ defined for the first bandwidth by the secondcommunication protocol, wherein D₁=N*D₂.
 13. The apparatus of claim 9,wherein the one or more integrated circuits are configured to generateeach OFDM symbol of the one or more OFDM symbols to further include afirst set of guard tones, and wherein the first set of guard tonesincludes a greater number of guard tones than a number of guard tones ina second set of guard tones, the second set of guard tones defined forthe first bandwidth by the second communication protocol.
 14. Theapparatus of claim 9, wherein the first bandwidth is 80 MHz, and whereineach OFDM symbol of the one or more OFDM tones includes 1024 tones. 15.The apparatus of claim 9, wherein the integer N is equal to four. 16.The apparatus of claim 9, wherein the one or more integrated circuitsare further configured to generate the data unit to include (i) the oneor more OFDM symbols and (ii) an extension signal field that follows theone or more OFDM symbols, wherein the extension signal field isgenerated using the second tone spacing defined for the first bandwidthby the second communication protocol.
 17. A method for generating a dataunit for transmission via a communication channel, the methodcomprising: generating, at a communication device, one or moreorthogonal frequency division multiplexing (OFDM) symbols, includinggenerating the one or more OFDM symbols based on a first tone mapcorresponding to a first number of OFDM tones or based on a second tonemap corresponding to a second number of OFDM tones, wherein the firsttone map is used if the data unit is to be transmitted in a firsttransmission mode corresponding to a first bandwidth or a secondtransmission mode corresponding to a second bandwidth, wherein thesecond bandwidth is twice of the first bandwidth, and the second tonemap used if the data unit is to be transmitted in a third transmissionmode corresponding to a third bandwidth or a fourth transmission modecorresponding to a fourth bandwidth, wherein the third bandwidth istwice of the second bandwidth and the fourth bandwidth is twice of thethird bandwidth; and generating the data unit to include the one or moreOFDM symbols in a data portion of the data unit.
 18. The method of claim17, wherein (i) the first bandwidth is 20 MHz, (ii) the second bandwidthis 40 MHz, (iii) the third bandwidth is 80 MHz, and (iv) the fourthbandwidth is 160 MHz.
 19. The method of claim 18, wherein (i) the firstnumber of OFDM tones is 256 tones, (ii) the second number of OFDM tonesis 512 tones, (iii) the third number of OFDM tones is 1024 tones, and(iv) the fourth number of OFDM tones is 2048 tones.
 20. An apparatus,comprising: a network interface device having one or more integratedcircuits configured to generate one or more orthogonal frequencydivision multiplexing (OFDM) symbols, including generating the one ormore OFDM symbols based on a first tone map corresponding to a firstnumber of OFDM tones or based on a second tone map corresponding to asecond number of OFDM tones, wherein the first tone map is used if thedata unit is to be transmitted in a first transmission modecorresponding to a first bandwidth or a second transmission modecorresponding to a second bandwidth, wherein the second bandwidth istwice of the first bandwidth, and the second tone map used if the dataunit is to be transmitted in a third transmission mode corresponding toa third bandwidth or a fourth transmission mode corresponding to afourth bandwidth, wherein the third bandwidth is twice of the secondbandwidth and the fourth bandwidth is twice of the third bandwidth, andgenerate the data unit to include the one or more OFDM symbols in a dataportion of the data unit.
 21. The apparatus of claim 20, wherein (i) thefirst bandwidth is 20 MHz, (ii) the second bandwidth is 40 MHz, (iii)the third bandwidth is 80 MHz, and (iv) the fourth bandwidth is 160 MHz.22. The apparatus of claim 20, wherein (i) the first number of OFDMtones is 256 tones, (ii) the second number of OFDM tones is 512 tones,(iii) the third number of OFDM tones is 1024 tones, and (iv) the fourthnumber of OFDM tones is 2048 tones.